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Discoveries of epithermal precious metal deposits
Journal o[ Geochemical Exploration, 27 (1987) 341-347
341
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Book Reviews
Discoveries of Epithermal Precious Metal Deposits, by V.F. Hollister (Editor). Case Histories of Mineral Discoveries; Volume 1. Society of Mining Engineers, A.I.M.E., New York, NY, 1985, 169 pp., US $63.50. Any effort to present information on the case histories of exploration and development of economically viable mineral deposits is to be applauded. However, only around 16% of the text of this volume is devoted to case histories of exploration. The majority actually consists of articles on geology that have been reprinted verbatim from readily available sources such as: Economic Geology, American Mineralogist, Mining Congress Journal, Engineering and Mining Journal, and U.S. Geological Survey Professional Papers and Circulars as well as Nevada Bureau of Mines and Geology Bulletins and Reports. The previously published material comprises approximately 60% of the text, has a median date of 1975, and ranges from 1959 to 1982. Of the four remaining "as yet not published" reprints, several have a distinct overlap with previously published versions (i.e., article by B.A. Mills on the Round Mountain gold deposit in Arizona Geological Society Digest, vol. XV). After excluding the largely previously published technical articles, the cost of information on the 14 case histories alone is over $2.50/page. Even including the four articles currently in review elsewhere ( Alligator Ridge, Getchell, Round Mountain, Toodoggone ), the cost of material presently not published elsewhere is greater than $1.00/page. The case history synopses range from 1 to 3 pages in length (24 pages total), and in quality from factually informative to retrospectively anecdotic. They all can easily be ingested quickly in any library that has already purchased this book. Coverage is divided into replacement-type deposits (8 cases total, largely sediment-hosted: Alligator Ridge, Candelaria, Carlin, Cortez, Getchell, Gold Acres, Jerritt Canyon, Northumberland) and volcanic-hosted deposits (6 cases total: Borealis, Round Mountain, San Bartolome, McDermitt, Queen Charlotte, Toodoggone). In a short preface, the editor presents an abstracted version of a general epithermal model that is oversimplified, out of date, and controversial. Unfortunately, no references, or further general reading suggestions for either additional specific data, or further factual information on the geology and geochemistry of epithermal systems are provided. The preface includes two very simplistic schematic cross sections; one for deposits in volcanic rocks, and one for sedimentary rocks. Although the figures lack scales, the depths of formation are reported to range between 100 and 1000 m below the "paleo-hotspring surface", and supposedly vary due to "boiling and telescoped zoning".
0375-6742/87/$03.50
© 1987 Elsevier Science Publishers B.V.
342
These same two reasons are used to explain the lack of the development of a paragenetic sequence in many deposits. Even though critical geologic spatial and temporal ties to a paleosurface such as constructive surficial sinters related to mineralization are distinctly lacking in at Carlin, Getchell, Cortez, Gold acres and most sediment-hosted deposits in general, the editor directly transposes the well documented and thoroughly studied epithermal hot-spring geologic setting for volcanic rocks to an analogous time-space setting in sedimentary rocks. This analogy apparently hinges on similarities in trace element associations ( Au, As, Sb, Hg and T1, etc. ), and equating the jasperoidal replacement of carbonate to relatively shallow subsurface silicification in some volcanic-hosted deposits. In addition, the K _+Alsilicate alteration zonation and increased base-metal values with depth, which are virtual trademarks of many volcanic-hosted deposits, are also reported to exist in the sediment-hosted environment in roughly similar spatial geometries with respect to gold ore, despite the fact that significant base-metal sulfides at depth, an outer propyllitic halo in silty calcareous sedimentary rocks, or a proximal zone containing montmorillonite spatially associated with mineralization have not been documented in a typical "Carlin-type" geologic setting. The editor also interprets the presence of marcasite to define an upper temperature limit of 170°C which is not necessarily consistent with recent information ( Murowchick and Barnes, 1986). In the introduction the editor suggests that the seeds of the present epithermal model were planted over 50 years ago, and that whereas modern contributions have refined and "perfected" the model, they have not fundamentally changed it. Whether a given model is good or bad is reflected in its utility in effective exploration. Any specific working exploration or genetic model is a reflection of the sum of our current geological and geochemical understanding, and therefore merely represents the present working hypotheses. Good models, such as for classic volcanic-hosted hot-spring deposits, evolve slowly and stand the test of time; however, they must also maintain an inherent flexibility for revisions provided by additional data and new discoveries. As a consequence, no model, regardless of how effective in exploration, is ever perfect or complete. To think otherwise could preclude additional scientific or economically viable mineral discoveries. The specific title of this volume is misleading because it strongly suggests exploration geologists are the intended audience. In addition, the full title implies this is the first of a series. More complete articles containing specific information on methodologies and results of both successful and failed exploration case histories would be a welcome, and much needed contribution to the literature. However, the format of this first volume largely provides material that is already at the disposal of actively engaged precious metal explorationists. It could possibly be of use to geologists overseas with less ready access to western literature. Given the high cost and paucity of new material in this
343 volume, and more recent information on epithermal systems in general, as well as technical articles with additional data on many of these 14 deposits, I regret to say that this book does not receive a high priority on a recommended purchase list. Reference: Murowchick and Barnes, 1986. Marcasite precipitation from hydrothermal solutions. Geochim. Cosmochim. Acta, 50 (12): 2615-2629. C A R L A. K U E H N (University Park, PA, U.S.A.)
Prospecting in Areas of Desert Terrain. The Institution of Mining and Metallurgy, London, England, 1985, 283 pp., £ 28 (ca. US $45 ). Depending on whose definition one chooses to use, between 14 and 22 perent of the Earth's continental surface is classified as "desert." This constitutes an area ranging from 20 to 31 million km 2. From this standpoint alone, a book concerning strategy, planning, and execution of multidisciplinary mineral exploration programs in desert environments should be of some importance to explorationists in general asnd to exploration geochemists in particular. This book is a collection of 26 papers presented at the international conference, "Prospecting in areas of desert terrain," organized by the Institution of Mining and Metallurgy and the Ministry of Energy and Mines, Government of Morocco, with the cooperation of the Arab Organization for Mineral Resources. The conference was held in Rabat, Morocco, on April 14-17, 1985. As might be expected given the conference site, the deserts of northern Africa and Arabia receive the most attention: seven and six papers, respectively. The deserts of southern Africa and Australia are the focus of four and three papers, respectively, and those of Chile, northwest India, and Iran are each the location of one study. The three remaining papers in the volume discuss geophysical and geochemical instrumentation appropriate for arid regions and have no specific geographic focus. Fourteen of the papers are at least partially devoted to geochemical exploration. The exploration geochemist must deal with a number of problems when working in the desert. Logistics can be quite difficult in waterless, roadless, and uninhabited terrain. Secondary dispersion of pathfinder elements is generally limited in the poorly developed soils commonly found in arid climates. This factor may necessitate a higher sample density than would be needed in more humid areas. There is the ever-present problem of eolian contamination resulting in dilution of soil or stream sediments with barren, windblown material. Four methods that have been successful in combating the dilution problem are discussed in this volume: (1) separating and discarding the eolian
341
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
Book Reviews
Discoveries of Epithermal Precious Metal Deposits, by V.F. Hollister (Editor). Case Histories of Mineral Discoveries; Volume 1. Society of Mining Engineers, A.I.M.E., New York, NY, 1985, 169 pp., US $63.50. Any effort to present information on the case histories of exploration and development of economically viable mineral deposits is to be applauded. However, only around 16% of the text of this volume is devoted to case histories of exploration. The majority actually consists of articles on geology that have been reprinted verbatim from readily available sources such as: Economic Geology, American Mineralogist, Mining Congress Journal, Engineering and Mining Journal, and U.S. Geological Survey Professional Papers and Circulars as well as Nevada Bureau of Mines and Geology Bulletins and Reports. The previously published material comprises approximately 60% of the text, has a median date of 1975, and ranges from 1959 to 1982. Of the four remaining "as yet not published" reprints, several have a distinct overlap with previously published versions (i.e., article by B.A. Mills on the Round Mountain gold deposit in Arizona Geological Society Digest, vol. XV). After excluding the largely previously published technical articles, the cost of information on the 14 case histories alone is over $2.50/page. Even including the four articles currently in review elsewhere ( Alligator Ridge, Getchell, Round Mountain, Toodoggone ), the cost of material presently not published elsewhere is greater than $1.00/page. The case history synopses range from 1 to 3 pages in length (24 pages total), and in quality from factually informative to retrospectively anecdotic. They all can easily be ingested quickly in any library that has already purchased this book. Coverage is divided into replacement-type deposits (8 cases total, largely sediment-hosted: Alligator Ridge, Candelaria, Carlin, Cortez, Getchell, Gold Acres, Jerritt Canyon, Northumberland) and volcanic-hosted deposits (6 cases total: Borealis, Round Mountain, San Bartolome, McDermitt, Queen Charlotte, Toodoggone). In a short preface, the editor presents an abstracted version of a general epithermal model that is oversimplified, out of date, and controversial. Unfortunately, no references, or further general reading suggestions for either additional specific data, or further factual information on the geology and geochemistry of epithermal systems are provided. The preface includes two very simplistic schematic cross sections; one for deposits in volcanic rocks, and one for sedimentary rocks. Although the figures lack scales, the depths of formation are reported to range between 100 and 1000 m below the "paleo-hotspring surface", and supposedly vary due to "boiling and telescoped zoning".
0375-6742/87/$03.50
© 1987 Elsevier Science Publishers B.V.
342
These same two reasons are used to explain the lack of the development of a paragenetic sequence in many deposits. Even though critical geologic spatial and temporal ties to a paleosurface such as constructive surficial sinters related to mineralization are distinctly lacking in at Carlin, Getchell, Cortez, Gold acres and most sediment-hosted deposits in general, the editor directly transposes the well documented and thoroughly studied epithermal hot-spring geologic setting for volcanic rocks to an analogous time-space setting in sedimentary rocks. This analogy apparently hinges on similarities in trace element associations ( Au, As, Sb, Hg and T1, etc. ), and equating the jasperoidal replacement of carbonate to relatively shallow subsurface silicification in some volcanic-hosted deposits. In addition, the K _+Alsilicate alteration zonation and increased base-metal values with depth, which are virtual trademarks of many volcanic-hosted deposits, are also reported to exist in the sediment-hosted environment in roughly similar spatial geometries with respect to gold ore, despite the fact that significant base-metal sulfides at depth, an outer propyllitic halo in silty calcareous sedimentary rocks, or a proximal zone containing montmorillonite spatially associated with mineralization have not been documented in a typical "Carlin-type" geologic setting. The editor also interprets the presence of marcasite to define an upper temperature limit of 170°C which is not necessarily consistent with recent information ( Murowchick and Barnes, 1986). In the introduction the editor suggests that the seeds of the present epithermal model were planted over 50 years ago, and that whereas modern contributions have refined and "perfected" the model, they have not fundamentally changed it. Whether a given model is good or bad is reflected in its utility in effective exploration. Any specific working exploration or genetic model is a reflection of the sum of our current geological and geochemical understanding, and therefore merely represents the present working hypotheses. Good models, such as for classic volcanic-hosted hot-spring deposits, evolve slowly and stand the test of time; however, they must also maintain an inherent flexibility for revisions provided by additional data and new discoveries. As a consequence, no model, regardless of how effective in exploration, is ever perfect or complete. To think otherwise could preclude additional scientific or economically viable mineral discoveries. The specific title of this volume is misleading because it strongly suggests exploration geologists are the intended audience. In addition, the full title implies this is the first of a series. More complete articles containing specific information on methodologies and results of both successful and failed exploration case histories would be a welcome, and much needed contribution to the literature. However, the format of this first volume largely provides material that is already at the disposal of actively engaged precious metal explorationists. It could possibly be of use to geologists overseas with less ready access to western literature. Given the high cost and paucity of new material in this
343 volume, and more recent information on epithermal systems in general, as well as technical articles with additional data on many of these 14 deposits, I regret to say that this book does not receive a high priority on a recommended purchase list. Reference: Murowchick and Barnes, 1986. Marcasite precipitation from hydrothermal solutions. Geochim. Cosmochim. Acta, 50 (12): 2615-2629. C A R L A. K U E H N (University Park, PA, U.S.A.)
Prospecting in Areas of Desert Terrain. The Institution of Mining and Metallurgy, London, England, 1985, 283 pp., £ 28 (ca. US $45 ). Depending on whose definition one chooses to use, between 14 and 22 perent of the Earth's continental surface is classified as "desert." This constitutes an area ranging from 20 to 31 million km 2. From this standpoint alone, a book concerning strategy, planning, and execution of multidisciplinary mineral exploration programs in desert environments should be of some importance to explorationists in general asnd to exploration geochemists in particular. This book is a collection of 26 papers presented at the international conference, "Prospecting in areas of desert terrain," organized by the Institution of Mining and Metallurgy and the Ministry of Energy and Mines, Government of Morocco, with the cooperation of the Arab Organization for Mineral Resources. The conference was held in Rabat, Morocco, on April 14-17, 1985. As might be expected given the conference site, the deserts of northern Africa and Arabia receive the most attention: seven and six papers, respectively. The deserts of southern Africa and Australia are the focus of four and three papers, respectively, and those of Chile, northwest India, and Iran are each the location of one study. The three remaining papers in the volume discuss geophysical and geochemical instrumentation appropriate for arid regions and have no specific geographic focus. Fourteen of the papers are at least partially devoted to geochemical exploration. The exploration geochemist must deal with a number of problems when working in the desert. Logistics can be quite difficult in waterless, roadless, and uninhabited terrain. Secondary dispersion of pathfinder elements is generally limited in the poorly developed soils commonly found in arid climates. This factor may necessitate a higher sample density than would be needed in more humid areas. There is the ever-present problem of eolian contamination resulting in dilution of soil or stream sediments with barren, windblown material. Four methods that have been successful in combating the dilution problem are discussed in this volume: (1) separating and discarding the eolian