06
Dec
13

The Book

LodeVeinCover
LAST UPDATE: 29 October 2014   PUBLISHING CONTRACT NEGOTIATIONS WITH ELSEVIER IN PROGRESS

How do gold deposits form and how do you find more ore?

THE METALLOGENY OF LODE GOLD DEPOSITS: A SYNGENETIC PERSPECTIVE

This book is a treatise on the formation of vein or lode gold deposits, which historically have accounted for about 75% of worldwide gold production. Each of the 12 chapters also has a brief summary for brokers, investors, promoters and geology students. It describes all aspects of the geology of gold vein formation. Existing formation theories are reviewed but the main thrust of the book centers on discovery of a paradigm shifting geological process. This which was unearthed over a period of 30 years by following subtle clues that the mainstream geological fraternity has interpreted differently. Very powerful new exploration tools are the result. While they cannot be patented, they have proven useful in a worldwide search for gold deposits and to find extensions of existing mines and mining districts. One potential mine has already been found. The book is over 80% complete and all key chapters are finished. A publication contract is imminent with a major publisher of academic books. The book expands on a paper published by the author in the conference proceedings for WorldGold2011 held in Montreal under the auspices of The Canadian Institute of Mining and Metallurgy.(Downloads) There are numerous diagrams and photos to illustrate the theme. Anyone interested in how gold deposits form and how to find more ore will welcome this book. It is essential reading for gold mining exploration companies, brokerage firms specializing in gold, entities such as the World Gold Council or Sprott Equities. In particular it will be of interest to out-of-the-box thinking exploration geologists, academics,  entrepreneurs and financiers who appreciate more than most, the advantages to early adoption of new ideas. The book provides a practical guide to ore!

Continue reading ‘The Book’

24
Mar
14

Lode Gold Deposits: Preface, Summary, Dedication & Acknowledgements



fig-3a

In this  photo of quartz beds in a turbidite sequence on Markie Point, Nova Scotia,  I have subdivided and  numbered quartz (Q), turbidite muddy pelite (E) and basal greywacke (A). E1 underlies E3. Hammer tip points in facing direction.  Bedded quartz almost always occurs in the E pelitic-pelagic units or at the contact with overlying massive sandy greywacke (Unit A). This Q-E-A asymmetry is characteristic of most lode gold veins and is a powerful tool for following stratigraphy and unravelling structure. This book is devoted to investigating  the processes that underlie this observation.

NEWS FLASH: ELSEVIER HAS AGREED TO PUBLISH THIS BOOK BASED ON FOUR HIGHLY FAVOURABLE REVIEWS OF MY PROPOSAL! CONTRACT NEGOTIATIONS ARE IN PROGRESS! UPDATES AND TIME LINE TO PUBLISHING, WILL BE POSTED HERE.

PREFACE AND SUMMARY  13 November 2014

This book records a journey of trying to understand the metallogeny (ie genesis in time and space) of lode gold deposits. For me this began in 1982 when I saw excellent sea-shore exposures in SE Nova Scotia, where ubiquitous quartz outcrops that is characteristic of Meguma turbidite-hosted gold deposits. I had read much of the literature on their origin, including the comments of T. Sterry Hunt (1868) who said that: “ I think that to describe them otherwise than as interstratified beds would be to give a false notion of their geognostic relations. The laminated structure of many of the lodes, and the intercalation between their layers of thin continuous films or layers of argillite, can hardly be explained in any other way than by supposing these lodes to have been formed by successive deposition of what was, at the time, the surface of the earth.”

I found no convincing contrary evidence during a summer of field work nor during extensive discussions with the late structural geologist Jack Henderson nor the late Simon Haynes both of whom worked in the same area at the same time. Published research from authorities who hold diametrically opposite epigenetic views on their genesis was also not compelling. A report to the Geological Survey of Canada summarized my findings. Among other ideas, sea-floor hydrothermal hot springs presented a simple and compelling origin for Meguma quartz and lode gold veins. The report did not find favour and was not published at the time. It is reproduced in its entirety as Appendix A, because the ideas are just as relevant today and together with Appendix B, descriptions of veins constitute essential background to understanding the syngenetic ideas which underpin this book. Interestingly, my findings have not been duplicated by other researchers, although some excellent analytical and dating work has been done in the Meguma. In a rare instance, and at the expense of presenting conclusions before evidence, I think the statement of T. Sterry Hunt is as valid today as in was in 1868 because the “veins”  record the operation of basic geological processes.

Subsequently and over a period of several years, details of the processes involved have become increasingly clear. Careful mapping and field work underlies the thesis of this book. During intermittent mineral exploration programs in the Quebec portion of the Abitibi belt, Chester Twp (Côté Gold deposit) and the Beardmore gold districts in Ontario as well as the Maskwa batholith in Manitoba, and from detailed mapping and core logging, I noticed that these 3.2 to 2.7 Ga Archean rocks were also showing evidence for synvolcanic sea-floor hot spring formation. The evidence is subtle but pervasive that gold-sulfide-quartz veins formed at the same time as the enclosing host rocks and some form of syngenesis not only underlies Meguma turbidite-hosted deposits, but Archean volcanic-hosted lode vein deposits and indeed many lode deposits of all ages on a world-wide basis. This book records the steps that constitute proof of this claim. I present my evidence, with some trepidation, while trying to navigate objectively what I consider a hinterland of preconceptions in much lode gold literature. The task is made more difficult because deformation can result in saddle-reef, en-echelon and crack-seal veins and sorting out the extent to which this is related to gold deposit formation is one key to understanding their genesis. Indeed, some fundamental crustal processes are revealed. I hope the reader will not be put off by my fearless and iconoclastic interpretations.

My career in geology started as a geological assistant on regional Geological Survey of Canada Arctic mapping parties at a time when regional mapping was still being done. I also collected minerals and in trying to understand how they formed, developed a research interest in oxide and sulfide phase chemistry, especially of iron-titanium oxides (M. Sc. Kretschmar & McNutt, 1971) and arsenopyrite (Ph.D, Kretschmar & Scott, 1976). It has been a lifelong quest to try to understand the physical and chemical conditions of ore deposition and how to apply this knowledge in a practical way during a career in exploration geology.

The vast expansion of research and ready access to almost all technical papers through the Internet is unparalleled in the history of science and should in theory by now, have resulted in a complete understanding of the lode vein formation process. While many would not agree, I think that gold deposit research is model-rich and data-poor, and models are galloping off in all directions, in an apt analogy by Canadian humorist Steven Leacock.

The fragmented nature of gold formation models is in part due to the declining importance of field work in the geosciences. There is a loss of data due to mining, as lower gold grades become economic and evidence is destroyed in open pits on the surface or in large underground drifts. As the gold price fluctuates, the fortunes of junior mining companies whose websites and reports often contain excellent descriptive data also fluctuate or disappear. On the positive side, the development of instrumental and analytical techniques e.g. XANES has permitted independent insights into early Archean sea-floor hydrothermal P-T conditions. The quest to understand primordial carbon in 3.2 Ga Strelly Pool cherts by NASA scientists, led to the realization that graphite and stylolite-like textures, both common in lode veins, have an abiotic origin. The carbon originates under P-T conditions that are similar to the Fischer-Tropsch industrial process. The “Caulifower Garden” of silica-rich, sulfide-free chimneys on the Galapagos Spreading Ridge is a modern example of quartz crusts forming on the sea-floor. Ethane in fluid inclusions has been used as another tracer to show fluids and gold were sourced from deeply buried carbon-rich, and pyrite-gold-bearing sedimentary rock. Pyrite frequently shows zoning which may reflect two periods of gold mineralization. Related research shows that theoretical heat-flow calculations and the thermodynamic properties of sea-water lead to sea-floor spacing of hydrothermal cells, that corresponds quite well with spacing and geometry of lodes observed from grade-thickness contours in gold mining camps.

Which elements of current lode gold formation models are compatible with syngenesis? How does one differentiate a brilliant academic construct from a model driving process? Correlation is not necessarily causation. I think it is clear that interpretations and models are unlikely to be valid if they are not grounded in careful field work.

What is this book? This book is intended as a synthesis of lode gold vein forming processes and to point out the commonality in similar deposits worldwide. My empirical model, is based on  widely known and accepted principles of ore deposition and shows how they apply in a felsic “intrusion” environment. A large part of the book is based on detailed outcrop maps and photos of field occurrences and textures. All my interpretations flow directly from field work and the querying of underlying physical processes and interpretations in the literature. Geological descriptions represent a slice in time. Often key outcrops in mining camps are only exposed for a limited time and much detailed and potentially valuable geological data may be lost. Stripped outcrops are covered again because of environmental regulations, abandonment of the project or they may be mined out in increasing large and lower grade open pits.

In recent history, there have been many developments that have aided ore deposit research. These include: the development of microprobe and sophisticated analytical instruments which produce increasingly lower detection limits and more accurate and precise analyses, the large field of stable isotopes, age dating, detailed understanding of continental drift, discovery of sea-floor hydrothermal systems, and the development of T-fS2 space and Paul Barton’s concept of ore forming environment. Much excellent recent work has illuminated geological and chemical conditions accompanying  gold formation. e.g. Witwatersrand mineral mapping and the mineral zoning studies on Carlin deposits showing two separate mineralizing events. In parallel, there is in evidence a disturbing disconnect between exploration geologists and academe. In the 1970s and 1980s field-oriented explorationists tended to more readily accept syngenetic concepts for lode gold deposits. Today, such ideas are heretical and have been virtually expunged from the literature. There is increased specialization resulting often in substantially different interpretation of a given outcrop or map area.

What this book is not: it does not present a balanced view because I think that intrinsic to a “syngenetic mindset” is alternate vocabulary to translate and decipher the currently dominant and fashionable language of structure and epigenesis. Indeed the book is entirely oriented towards syngenesis because as I hope will become evident, the majority of lode veins -a definition of which is important – formed at the same time as the enclosing rocks. Fluid remobilised during lithification, deformation and metamorphism has been suggested to add to gold endowment in some deposits and may upgrade a sub-economic resource to mineable status. Excellent evidence for the magnitude and importance of this process is only now emerging particularly for Carlin-type deposits and the Witwatersrand, but it will be seen that deformation and metamorphism neither invalidate a syngenetic origin nor are required for the formation of a gold deposit.  Hydrothermal fluids may be metamorphogenic or magmatic.

The book has twelve chapters and four appendixes.  After a review of gold formation models (Ch.1),  and  a description of  vein textures in outcrop (Ch. 2),  the new concept of “Gold Cycles” (Ch.3) is defined. Its application and detailed and representative  field descriptions(Ch. 4) lead  to an understanding of  “lamprophyres” (Ch.5).  In turn, the relationship of lode deposits to felsic “intrusions” and TTG lithologies (Ch. 6) emerges from application and  understanding  “Gold Cycle E” or GCE units. A review of chemical, thermobarometric and age dating principles provides the framework for vein formation conditions (Ch. 7). A simple syngenetic formation model (Ch. 8) and select ore deposit descriptions (Ch. 9) provide further insights into lode vein formation and exploration applications (Ch. 10). The palaeogeological environment of lode vein formation (Ch. 11) leads to a critical examination of syngenesis within the context of current worldwide lode gold research (Ch. 12). In somewhat greater detail:

In CHAPTER 1, review of numerous models in the literature reveals consensus that there is an elusive process, which has prevented complete understanding of lode gold formation process. It has even been recently stated that lode gold deposits are amagmatic or unknown. What is the timing of vein formation and the origin of the hydrothermal fluid? This is unlike for instance in komatiitic nickel formation, for which in an equivalent time period, say from 1968 when komatiites were first identified, to the present, an excellent understanding has emerged as well as a general agreement on a formation model. Reviewing the historical aspects of syngenetic ideas for gold deposit formation it becomes apparent that they are almost completely absent from current main stream thought. There is a strong polarization towards a metamorphogenetic origin of fluids, deep seated faults to focus the fluids, and structural traps where the lode veins are sited. Rarely voiced objections to a syngenetic origin for lode veins include absence of feeder veins, disequilibrium between vein and wall rock, younger vein ages and high fluid inclusion formation pressures which preclude a sea-floor origin. These are valid concerns, but more common is wholesale dismissal of the concept, which I attribute to a combination of an Agricola-Lindgren-Ramsay factor, Bowen’s influence, the geologist’s propensity for model making and giving disproportionate weight to experimental and theoretical results over what your eyes are telling you.
CHAPTER 2, forms the basis of the syngenetic perspective on textures that I bring to this book. Unless there is evidence to the contrary, what we see in outcrops is primary. Imagine the proverbial man from Mars looking at an A-E turbidite containing quartz “veins” on a sea-shore in the Meguma of Nova Scotia. In the absence of preconceptions (also known as previous work with a contrary view), our Martian could considered the white rock as either primary or secondary. Therefore from a purely academic perspective, the idea that quartz formed at the same time as the enclosing rocks is a valid direction of inquiry. This is the premise (prejudice) on which the this book is based. To me detailed outcrop, trench maps and numerous photos of textures from the Meguma clearly show that silica was deposited often as a gel, and always as an integral element of turbidite sedimentation. Similar textures are seen in volcanic hosted veins. A rapid deposition rate may result in massive structureless quartz (bull quartz). Fine-scale monomineralic layering in quartz veins (crack-seal texture) reflects slow deposition and evolution of solutions over time. Breccia veins are possible feeders. Vein complexity and cross-cutting relations increase near vents. Primary vein and sulfide textures are substantially preserved during deformation and metamorphism and what we see in outcrop provides crystal clear constraints on hypotheses for their origin.

In CHAPTER 3,  the observation that a majority of lode veins occur at the top of graded bedding cycles is expanded to the concept of gold cycles (GC), loosely based on turbidite formation and terminology. Most quartz occurs with within or on top of E-division pelagic-pelitic (or tuffaceous) units in Bouma-like A-E turbidites. In gold camps, I give “E” division units the name Gold Cycle “E” or GCE which in another large leap, I suggest that these interflow sediments or “auriferous exhalites” are often mistaken as “shear zones”, “lamprophyre” or “mafic dikes”. In volcanic terrain “E” units have a basaltic composition. GC “A” division lithologies include mafic and felsic flows, granite, syenite, TTG suite and epiclastics. The GC concept systematizes and simplifies description of bedding- parallel quartz units (“veins”) and host rock. This permits wide recognition of Gold Cycles in the literature.

CHAPTER 4 provides further field observations for the syngenetic concepts that form the basis of this book. First, I describe and show by photos of quartz in the “E” division of Bouma turbidites in outcrops how Meguma and by analogy, Ballarat and other bedding-parallel turbidite-hosted gold veins, can be interpreted as forming at the same time as the enclosing rocks. This concept was developed in a previously unpublished 1983 manuscript (reproduced in entirety as Appendix A) and is illustrated by photos (Appendix B). In the second part of Chapter 4 , I show that in drill core and in outcrop, GCE also occur in the much older 2,740 Ma Chester tonalite Complex (CC), which hosts the multimillion ounce Côté Gold deposit currently being developed by Iamgold. The presence of GC lithologies and graded bedding clearly demonstrates that the veins and gold were formed subaqueously. Gold-bearing strata can be traced for hundreds of metres through a thick pile of felsic flows. GCs are geopetal and permit mapping of faults and structure and tracing of  gold-bearing strata. This is followed by descriptions and a brief discussion of GCs and lode veins from the spectacularly high grade Archean Sage Gold-Prodigy (Kodiak) “Hercules” vein systems and extensions in the Elmhirst “intrusion” in the Beardmore-Geraldton greenstone belt of Ontario. From very close (50 m) drill spacing and logging the core on sometimes millimetre scale, it is possible to unravel structure, stratigraphy and sea-floor vent spacing parameters. High grade veins in the Little Bear Lake area of the Maskwa tonalite batholith in Manitoba are synvolcanic, their asymmetry can be used to unravel regional structure. They are hosted by rocks of the trondhjemite-tonalite-granodiorite (TTG) suite.

Highly relevant for lode vein formation models is an outcrop in the Chester Complex in which a lamprophyre (L) cross-cuts a Gold Cycle “E” (GCE) unit. I mapped this in detail and difference between them is explored extensively in CHAPTER 5, in which I examine the widely reported relationship between lode gold deposits and lamprophyres (L) using REE, trace element and whole rock analyses to clarify the role of Ls. L and GCE units are subtly but clearly different. They share broadly similar calc-alkaline affinity and a high degree of fractionation with elevated LREE and incompatible trace elements. Primitive Mantle and NMORB normalized plots also show significant depletion of Nb, Ta and Ti. However, basaltic (GCE) samples are more primitive, with higher concentrations of Mg, Cr, Ni & Ca and lower concentrations of Si, Al, Na and P. Lamprophyres also have higher concentrations of LREE and considerably lower concentrations of Au. I concur with previous workers that there is no genetic connection between lode gold deposits and lamprophyres, but if a true lamprophyre intrudes a gold-bearing sequence, assimilation may lead to above background gold concentrations. A well-documented example occurs in Red Lake. Confusing lamprophyre and GCE is not possible in a good outcrop exposure, but how do you know what is the origin of that green xenolith in a deformed felsic host? Many so-called lamprophyres in Abitibi-belt, Yilgarn block and other gold camps appear to be CGE units. This is the most important conclusion based on some 20 trace element ratios and petrographic plots. Chemistry alone cannot distinguish between CGE and lamprophyre but true lamprophyres are easy to recognize in good exposures. A short section addresses my findings that the chemistry of mafic dikes, or enclaves in TTG suite “intrusions”, such as the Maskwa batholith, the Bourlamaque batholith and the Chester Complex resembles mafic components of andesite-dacite-rhyolite (ADR) and TTG  suites. TTG rocks are widely considered to have a magmatic origin, with magmas formed under conditions of low pressure, dry melting and fluxing by hydrous fluids derived from subducted lithosphere. Can the ubiquitous GCE pelagic-pelitic strata in these “intrusions” help towards understanding their formation ? Their enigmatic genesis has been the subject of 35 years of research. TTG suite rocks often are older than surrounding volcanics and one possible line of investigation is to invoke early felsic volcanism, now exposed by folding as basement to Archean greenstone belts . The Maskwa batholith in Manitoba is an example. Consequences for TTG formation models are significant but are not discussed in detail.

My claim that GCEs are time-stratigraphic volcano-sedimentary markers that subdivide flows and flow sequences, naturally leads to question the nature of their felsic host rocks. Their common presence in felsic-hosted gold deposits is further clear evidence of felsic submarine extrusive volcanism. This is explored in CHAPTER 6 in context of an area within the Chester Complex that is a stratigraphic extension of the Côté Gold deposit. Major lithologies in the Chester “trondhjemite-diorite laccolith”, which hosts the Côté Gold deposit of IMG (Iamgold), are bi-modal volcanics with SiO2 contents ranging from 51-77%. A database of >200,000 assays, trace elements and high resolution photos of >4,000 m of core from drilling on Clam Lake (Appendix C) was used to correlate stratigraphy and mineralization over hundreds of metres between drill holes. Scandium is a useful proxy for silica and its concentration is inversely related to SiO2. Gold is hosted by GC interflow sediments which may contain quartz (veins) or silica exsolved from felsic flows. The Côté Gold deposit is not an Archean copper-gold porphyry, as proposed in current publications, but it occurs in a limb of a northwest trending steeply south-dipping overturned bi-modal volcanic sequence.

In CHAPTER 7, I selectively examine and review chemical, isotopic and age dating literature to place the syngenetic formation mode into a P-T-x framework. Experimental and theoretical calculations from the seawater-quartz system shows that gel precipitation is possible in the temperature formation range commonly shown by fluid inclusions. The difficulties of using fluid inclusion data to delineate formation pressures are well known. High fluid inclusion pressures are based on theoretical calculations and assume equilibrium with quartz, which may not be true. Kinetic factors are important. Fluids apparently rise nearly adiabatically from a deep reaction-zone where they are in equilibrium with quartz at high temperature and pressure. During rapid upwelling, quartz nucleation is suppressed and dissolved silica ends up being flushed out into the ocean. Amorphous silica or quartz in mounds or chimneys attests to a process that allows nucleation of silica to occur and one possibility is that fluid encounters a regime of slower and more diffuse flow, perhaps combined with substantial conductive heat-loss. Quartz decrepitation studies reveal the role of CO2 in gold precipitation. Silica solubility increases with pressure. The interaction of hot dense brines with seawater, and non-linear density effects can cause buoyancy reversals on cooling. This in turn can lead to a dense brine pool with hydrostatically stable stratification and double diffusive layers from which silica gel can precipitate. The precipitation of gold from hydrothermal solution is well studied.  fO2 and fS2 diagrams show a solubility cliff for gold that define precipitation conditions.  Sulfide phase chemistry shows the general position of lode gold forming conditions within Barton’s ore forming environment. Zoning in arsenopyrite in Meguma veins and sediments is a probable result of non-equilibrium growth, differences in S and As availability and diffusion kinetics. Therefore the high temperatures obtained from the arsenopyrite geothermometer are not meaningful for zoned arsenopyrite formed in a low temperature in diagenetic sedimentary environment. XANES analyses of stromatolite-like structures in 3.45 Ga Strelly Pool cherts in the Pilbara craton show that carbonaceous material and graphite – common in gold-bearing lode veins – was abiotically generated at 2-300o C and 550 bars pressure. This is independent evidence for a link to sea-floor vents. Such carbon is common in lode gold veins. Age dates for bedding parallel lode veins and host rocks coincide in several well-studied examples. In other instances where they do not, what was dated and the techniques should be re-examined before discrepancies can be considered as evidence against syngenesis. How are Re-Os dates on diagenetic arsenopyrite affected by non-equilibrium As/S zoning? To what extent has metamorphism and intrusion reset vein formation ages? Fluid P-T-X parameters for lode veins are well constrained and both metamorphic and magmatic hydrothermal fluids are compatible with syngenesis.

An empirical model for syngenetic formation of lode veins is presented in CHAPTER 8. It is characterized by simplicity. Sea-floor hydrothermal vents and seeps are buried by periodic influx of detrital, pyroclastic material or flows. This “new” empirical syngenetic model for LV formation focuses on the role of silica, stratigraphy, sedimentology, fertile “recycled” crust as a gold source, bimodal felsic-mafic volcanism and combines new insights from sea-floor hydrothermal systems and crustal formation processes. All you need is a source bed and heat from an elevated geothermal gradient (mantle plume?), crustal subsidence or subduction . In the deposition environment key variables are gold, base metal, SiO2 and CO2 content and NaCl (density) of the original fluid. Lode vein forming silica-rich fluids rise nearly adiabatically from a deep reaction-zone where fluids are in equilibrium with quartz at high temperature and pressure. In scenario A, during rapid upwelling, quartz nucleation is suppressed and dissolved silica ends up being flushed out into the ocean. In Scenario B, nucleation of silica occurs and vein formation results during slower and more diffuse flow, combined with substantial conductive heat loss. Economic gold deposits result from a favourable interplay of gold-rich hydrothermal solution, seafloor vent geometry and deposition parameters, boiling, depressurization and dilution at the site, sedimentation and burial by volcanics or clastic sediments. Keep the hydrothermal cell operating long enough (say 40 my) and you may get a large or giant deposit (e.g. Homestake). Even 10 million years is long enough as is shown by recent dating of Blake River volcanics which host major Abitibi belt Au-rich VMS deposits.

CHAPTER 9 presents select case studies of well-characterized gold deposits mainly from Archean shield areas that to me illustrate aspects of syngenetic formation, such as their stratabound nature, the presence of Gold Cycles and asymmetric alteration. Drill cross-sections and mine grade-thickness plots allow detailed delineation of vent geometry, bottom topography and whether hydrothermal solutions emanate from a point source, multiple diffuse seeps or parallel fractures. Lode veins generally range from 250 to 600 m and up to 1,800 m in length. Larger lode veins may be 1-3 km long, 1-10 m thick and can be disc-shaped or lobate. Porous tuffaceous substrate may indicate silica saturation, which reflects diffuse venting, colloidal silica or exsolution of silica-rich fluids. One or two deposits are described from major shield areas. Mafic hosted deposits include Akasaba, Clavos, Eau Claire, Eagle River, Northern Empire, Omai and Lamaque. Felsic-hosted deposits include Goldlund, Bourlamaque, Côté Gold, Magino, Hammond Reef, Goldex, Maskwa, and Kodiak Golden Mile. Dingman is a carbonate-hosted Grenville age deposit in Southern Ontario.

CHAPTER 10 examines and presents exploration applications and examples how Gold Cycles, asymmetry and the geopetal nature of veins can be used in the field to determine regional stratigraphy, structure and aid with interpretation of geophysical data. Exploration applications of a syngenetic formation mode for lode vein deposits are numerous and to delineate and enumerate  them is one of the main objectives of this book. Recent recognition that the Abitibi belt developed autochtonously, has resulted in a correlative unconformity-bounded stratigraphic model which provides regional and deposit-scale stratigraphic intervals to explore for syngenetic mineralization. TTG rocks are targets and GCE and asymmetry can help unravel stratigraphy and structure. Theoretical and observed sea-floor fracture spacing (commonly 200-450 m) can reduce the cost of initial exploration drilling. Basin analysis and pyroclastic fragment mapping can be used for exploration. District-wide alteration halos may be detected by remote sensing, rock geochemistry, oxygen isotopes and quartz decrepitometry. Vent tracing techniques can be developed by using interflow (GCE) sediment composition, Fe/Mg ratio in carbonate, copper content in pyrite, Au/Ag ratios in electrum, proportion of quartz in GCE and vertical and horizontal changes in vein mineralogy.
CHAPTER 11 examines  palaeogeological environments for bi-modal volcanic and turbidite-hosted veins. In felsic-hosted deposits such as Côté Gold, fine- grained pelagic and hemi-pelagic sediments (GCE) in a volcanic setting indicate an intra-oceanic setting away from landmasses. Massive felsic and mafic lavas indicate intermediate to high discharge rates. Paucity of pyroclastics or explosive fragmentation, as well as peperite, indicate deep water. Fischer-Tropsch P-T parameters indicate water or reaction zone depths of 500- 2000 m and open space fillings with euhedral quartz in veins are suggestive of sea-floor or sub-seafloor boiling. A short section is devoted to a preliminary comparison of GCE chemistry to Archean interflow sediments and GLOSS or MUQ. Archean sagduction, isoclinal folding and deformation accompanying granitic intrusion accounts for the steep dip of most lode veins. Deformation and erosion expose veins but deformation has no genetic importance.

A critical analysis of existing models, conclusions and suggestions for further work form the subject of CHAPTER 12.  Much confusion in the gold deposit literature and generations of scientific data is resolved if the origin of lode veins is considered from a syngenetic perspective, even though important questions remain. Contentious issues involve age dates that are younger than the host rock, the importance of  remobilization, multiple vein generations and the applicability of syngenetic concepts to iron formation hosted or Carlin-type deposits. Vent tracing techniques can be refined, stratigraphy, structure and deformation, basin analysis, age dating and volcanic architecture all are key to an understanding of the lode vein environment. With a “syngenetic mindset”, new exploration and research directions for lode gold and other ore forming environments become apparent.

Dedication

This book is dedicated to those who have told me that until they heard my ideas, they did not understand the origin of lode vein deposits. It is dedicated to the students with million dollar instruments at their disposal who have never walked through the bush while trying to understand quartz vein formation. It is dedicated to the student with an advance degree from a prestigious university who when asked to write a field description of a gold showing, returned to me with a one page list of the deformation alphabet, but failed to mention what was the host rock type.

My advice above all, is that you must go into the field and let what you see underfoot lead you to your theories and supplement this with the literature. You will not be able to distinguish felsic flows from intrusive granite with a similar chemistry, unless you get out in the field. You will not be able to distinguish intrusive lamprophyres from pelagic-pelitic interflow sediments unless you see these rocks the field.

Finally, I dedicate this book to those geologist everywhere who are interested in understanding and finding lode gold deposits. I cannot claim originality, since every single observation has been previously made, but the significance has not necessarily been realized. My quest started out by simply stating the to me obvious: quartz veins in the Meguma formed at the same time as the enclosing rocks. This is neither a popular nor a balanced view, but I think the rocks themselves provide eloquent evidence in favour of syngenesis.

Acknowledgements

This book has had a long gestation period. My 1983 report which contained what I considered abundant evidence for a syngenetic origin of Meguma gold deposits was not published by the Geological Survey of Canada. Since then encouragement from gold experts has failed to materialize but some exploration geologists have been more receptive. A genuine ray of light was provided by George Langdon and Gerard Edwards of Shoal Point Energy, Bill Love of Sage Gold, and Roy Choi of GStar Mining who generously funded some of my iconoclastic ideas and gave permission to publish them. Sanatana Resources Inc. paid for chemical analyses and imposed minimal reporting requirements during an extended consultancy. Frank Racicot helped significantly with mapping and sampling. Steve Scott provided invaluable access to University of Toronto library facilities and made helpful comments on aspects of an earlier draft and has been consistently encouraging. Greg Anderson provided insight into behaviour of quartz in the silica-seawater system. A review by Stephanie Brueckner of the World Gold 2011 paper helped  improve the manuscript. John Ayer helped with petrographic plots and along with Hadyn Butler, Ken Collerson, Peter Laznicka, Derek McBride, Andreas Mueller, Franco Pirajno, Walter Pohl, Laurence Robb provided insightful comments on parts of the manuscript. Contributions from the LinkedIn and Research Gate web site discussion groups also helped. Most importantly, years ago, Dick Hutchinson, the most dedicated of syngeneticists, urged me to never give up! And finally, my wife Laura Carter will probably welcome my return from the basement. All errors are definitely my own.

06
Dec
13

Meguma

 

14-HarriganCove

 

This section is taken from:
Kretschmar, U.H. (2011) Syngenetic Gold: Lode Vein Geology and Exploration Implications. (in) World Gold 2011. Proceedings of the 50th Annual Conference of Metallurgists of CIM. Montreal, Canada. Edited by G. Deschênes. R. Dimitrakopoulos, J. Bouchard. pp 849-863.

A revised version constitutes Chapter 4.1 of  The Geology of Lode Veins: A Syngenetic Perspective

EXAMPLES OF “GOLD CYCLES”

Meguma Turbidite-Hosted Gold Veins and The Sedimentary Environment

Cambro-Ordovician Meguma gold deposits have been the subject of numerous studies. For widely accepted views of their genesis, see Kontak, Horne, and Smith [23], and Sangster and Smith [24]. They are considered part of the “greenstone clan” of gold veins, formed at depth from solutions, remobilized during deformation. The host Meguma Supergroup, discussed by Waldron et al. [25] is described as a thick (>10 km thick Cambrian to Early Ordovician turbiditic clastic succession, with a lower, coarser grained Goldenville Formation containing numerous quartz and lode gold veins and an upper, dominantly fine-grained Halifax Formation.

During a 1982 Canada-Nova Scotia Mineral Agreement project in NTS 11D16 and 11E1, detailed mapping was carried out by the author in gold districts and on seashores with excellent exposures, within the area shown in Fig. 2.

Fig. 2

Figure 2 – Location of seashore exposures and Meguma study areas, South Coast, Nova Scotia.

This unpublished work (Kretschmar [26, 27]) is referenced by Crocket et al. [28] and incorporated in part by Haynes [29]. The main claims are that bedding-parallel veins, which host 90% or more gold deposits are silica crusts deposited mainly in the form of a gel from hydrothermal solutions on the Cambro-Ordovician sea floor. The author suggests that deposition of quartz is terminated by episodic influx of detrital material from turbidity currents. This empirical model was based on the subjective interpretation of textures: bedding parallel veins formed at the same time as the enclosing rocks. For the Meguma, Mawer [30] and virtually all other researchers express diametrically opposed views, with the notable exception of T. Sterry Hunt [op.cit.]. In Nova Scotia, low metamorphic grade, excellent seashore exposures and abundant drill cores yield much information. Bedding parallel veins are found almost invariably within the upper E division of Bouma turbidites, e.g. Fig. 3.

fig-3a

Figure 3A – Markie Point. Nova Scotia.  Typical shoreline exposure of Meguma turbidites with synsedimentary quartz veins (tops are to the left of the photo).

 

Markie Point, Nova Scotia. Synsedimentary quartz veins at top of Bouma A-E turbidites. Quartz was deposited probably as gel during ongoing pelagic sedimentation.  Precipitation from silica-saturated hydrothermal solution was terminated by next turbidite. Hydrothermal cell re-established itself and cycle was repeated, resulting in stacked quartz crusts or "veins".


Markie Point, Nova Scotia. Synsedimentary quartz veins at top of Bouma A-E turbidites. Quartz was deposited probably as gel during ongoing pelagic sedimentation. Precipitation from silica-saturated hydrothermal solution was terminated by next turbidite. Hydrothermal cell re-established itself and cycle was repeated, resulting in stacked quartz crusts or “veins”.

Figure 3B.– Markie Point.  Upper Ec division of Bouma turbidite (GC for gold-bearing veins) showing quartz vein with complex internal structure, overlain by 30 cm thick turbidite with graded bedding. Massive base of next overlying turbidite (T3A) is at top of photo. Individual units are numbered from base upwards adapting turbidite terminology. Outcrop location: NAD 83. UTM 20T, 0543478/496511 and Figure 2.

13-HarriganCove

Figure 4 – Harrigan Cove Gold District, trench map of turbidite-hosted gold-bearing quartz veins. Turbidites and A, E, and Q subdivisions are numbered individually from base upwards. (Mapping by U. Kretschmar, 1982)

Detailed mapping in Harrigan Cove (Fig. 4) provides significant insights into veins, quartz, and gold and turbidite sedimentation. Location, history, geology, Au and As distribution in Harrigan Cove turbidites are described by Crocket et al. [op. cit.]. Fig. 4 illustrates twelve turbidites in a Harrigan Cove trench. Quartz occurs within the E division of turbidites or at the contact with the overlying A. Arsenopyrite occurs throughout in A division greywacke as a diagenetic mineral. Crosscutting quartz consists of thin “angulars” that transgress stratigraphy for 3 m. or less. Bedding-parallel quartz shows complex internal structure, bulbous bases that appear to contour onto the pelagic-pelitic substrate and chlorite, sericite, and graphite on internal partings (described in detail by Mawer [op.cit.] and Kontak et al [op.cit]).

BeaverDamNSSyngeneticQuartzVein

Figure 5 – Polished slab of quartz vein stratum from  Beaver Dam Gold Deposit (location on Fig. 2). The vein is a crust on pelitic substrate (upper E division of a turbidite) and shows four or more domains- representing different episodes of deposition. Monomineralic sulfide layers and probable abiotic carbon require multiple episodes of deposition (see Strelly Pool chert discussion)

Overlying are thin shale partings deposited on an indented surface – hollows are filled with 3 or 4 mm thick accumulations of black shale, chlorite or pelitic material. Q2 is 1-2 cm of darker re-
crystallized quartz . They are separated by a thin, poorly-developed bedding surface with small amounts of clayey material. Separating the lower three quartz “domains” from the overlying fourth is a 3 mm thick pyrite-galena cap. The upper quartz “domain” consists of 7.5 cm of coarsely crystalline quartz with irregularly shaped conical inclusions, generally elongated perpendicular to bedding. The fragments are delicately laminated and individual laminae consist of graphite, sericite, or chlorite. The quartz filling interstices between these structures is whiter and less crystalline. Our empirical field- based observations on quartz veins in the Meguma support the 1868 conclusion of T. Sterry Hunt [op. cit.] who wondered how anyone could doubt that they formed at the same time as the enclosing rocks. Current research (e.g. Sangster and Smith [op.cit.]) will yield significant new insights into Meguma gold deposits if they are re-interpreted on that basis. Further support is provided by Archean lode veins from Beardmore.

06
Dec
13

Downloads

AbitibiRegionalGeology LODE GOLD VEIN BOOK

2014 May. GAC-MAC Meeting, Fredericton: Abstract

2014MayGAC-MAC Abstract

2012 November. University of Western Ontario, Colloquium Series: Abstract

2011: World Gold 2011, Montreal

1985: GSA Meeting. Providence, R.I. Abstract. 

1984: Meguma TGDG: Abstract

28
Nov
13

Exploration Applications

CANADA: BOURLAMAQUE BATHOLITH, ABITIBI BELT, VAL D’OR AREA

bourlamaque-5

This is one example of how facing direction indicators provided by the asymmetry of Q-E-A Gold cycles can be used to unravel regional structure, narrow down the  search area  and point to potential targets.

The example is taken from the publication:  Kretschmar, U.H. (2011) Syngenetic Gold: Lode Vein Geology and Exploration Implications. (in) World Gold 2011. Proceedings of the 50th Annual Conference of Metallurgists of CIM. Montreal, Canada. Edited by G. Deschênes. R. Dimitrakopoulos, J. Bouchard. pp 849-863.

Eight mines in the Bourlamaque batholith are located on one or more  folded stratigraphic horizons. Structural correlation is based on Gold Cycle top determinations.  
The Bourlamaque Batholith and TTG Lithologies. The 10 x 25 km Bourlamaque batholith contains 8 mines. Campiglio and Darling [60] studied its chemistry and characterized it as a synvolcanic quartz tonalite. Its age is 2700 Ma (Wong et al. [61]). In a gravity study, Jebrak et al. [62], point out that it resembles a dyke rather than a sill – and confirm a distinct density difference between the northern and southern parts. Belkabir et al. [63] discuss the relation between “dikes” and “auriferous shear zones.” They indicate that complex shear zone and vein patterns within the pluton reflects the influence of diorite dikes. These acted as weak layers that were activated during subsequent deformation and illustrate the importance of layer anisotropy in auriferous shear zone development. The Beaufort mine was studied by Tremblay [64], the Ferderber mine by Vu et al. [65] and the gold potential of the Bourlamaque batholith by Taner and Trudel [66]. Current investigations on dating of veins are being carried out by Lemarchand et al. [67] showing strike, dip and spatial relationship of gold-bearing quartz veins to dikes. Daigneault and Gaboury [68] present a compilation of these studies.

Continue reading ‘Exploration Applications’

01
Oct
13

Formation Models

fig-15

This syngenetic model is based on grade-thickness contours of ore lenses, which shows how different ore-shoot geometry provides information about the sea-floor on which silica crusts are deposited. Hot dense saline brines sit in depressions or hollows and silica (hopefully with gold) precipitates as gel during conductive cooling. Only heat is needed as quartz and gold are leached from various rock types. Burial of the quartz crust may involve pyroclastics, volcanic flows or turbidity currents.

Traditionally Gold Formation Models fall into three main categories:

  1. those based on fluid composition and source of fluid.
  2. those based on structure and deposition site and mechanics of deposition e.g brittle-ductile transition or dilational jogs and
  3. those based on grade of metamorphism eg. greenschist-amphibolite transition.

Difficulties in the systematic classification of ore deposits stem from the large number of variables (lithological, structural, chemical and tectonic), which interact to make the observed data difficult to interpret. According to Frimmel (2007), a given deposit may be classified according to host rock (e.g. sediment-hosted), or according to a preferred genetic model (e.g. orogenic), the classification may emphasize a specific metal association (e.g. iron oxide copper gold), or it may be based on a comparison with a large prototype (e.g. Carlin type)’’. According to Bierlein (), who places importance on metamorphism, states there is still no consensus on a genetic model for gold deposits in metamorphic belts.  One point that can be stressed with some degree of certainty is that surface waters are unlikely to be important in the formation of ores. However, components of metamorphic, magmatic, and/or mantle processes may all play some role in ore genesis.

One purpose of this website is to provide a source of information on gold deposit models and in particular to update syngenetic concepts, which clearly have not been updated recently.




Welcome to the Syngenetic Gold Website

This website is dedicated to making better known syngenetic aspects of lode gold deposit genesis and to provide a source of information on theories of gold deposit formation.

In the 1970s and 1980s when models for VMS deposits invoked continental drift and sea-floor hydrothermal vents, models for gold deposit formation followed suit. Current formation models favour epigenetic origins. Over many years of research, I have accumulated much additional evidence that most lode gold veins represent silica and gold crusts, deposited from sea-floor hydrothermal vents. These were buried by periodic influx of turbidites, volcanic flows, or epiclastic equivalents. The strata were later folded and the original flat-lying beds are now steeply dipping "veins".

This simple model is at variance with current thinking but the implications for exploration are profound and the entire field of gold deposit genesis will benefit from applying syngenetic concepts to current models.

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