Hydrothermal ore-forming processes in the light of studies in rock-buffered systems; II, Some general geologic applications

Hemley, J. J.; Hunt, John Paul

doi:10.2113/gsecongeo.87.1.23

Cited by 186 publications

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“…Numerical modeling suggests that the dynamic evolution of permeability in the fracture network that develops above a porphyry intrusion is probably an important control on the localization of the precipitation front 68 . An additional sulfide precipitation mechanism, particularly in the later stages of hydrothermal evolution, is related to the neutralization of acidity in increasingly dissociated, cooling magmatic fluids by reaction with feldspars to form fine-grained white mica, illite and clays 69 . In order to form an economically exploitable porphyry orebody, fluids must be channelled through a relatively small volume of rock and the precipitation of metal sulfides must be very efficient within this volume (Box 4).…”

Section: Volatile Exsolution and Ore Formationmentioning

confidence: 99%

Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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Porphyry ore deposits source much of the copper, molybdenum, gold and silver utilized by humankind. They typically form in magmatic arcs above subduction zones via a series of linked processes, beginning with magma generation in the mantle and ending with the precipitation of metals from hydrous fluids in the shallow crust. A hierarchy of four key "triggers" involved in the formation of porphyry deposits is outlined. Trigger 1 (10 2 -10 3 km scale) is a process of cyclic refertilization of magmas in the deep crust. Trigger 2 (10 1 -10 2 km scale) is the process of sulfide saturation in magmas that can both enhance and destroy ore-forming potential. Trigger 3 (10 0 -10 1 km scale) relates to the efficient transfer of metals into hydrothermal fluids exsolving from porphyry magmas. Trigger 4 (~10 0 km scale) identifies processes that lead to the final precipitation of ore minerals. Although all processes are required to a greater or lesser degree, it is argued that trigger 3, as an over-riding mechanism, can best explain the restriction of large deposits to specific arc segments and time periods. Consequently, recognition of the fingerprint of sulfide saturation in igneous rocks may help mineral exploration companies to identify parts of magmatic arcs particularly predisposed to ore formation.Ore deposits are scarce. Their discovery consumes considerable time and resources and only about one in every one thousand prospects explored by companies is eventually developed into a mine. Deposits often occur in clusters and formed within specific time intervals. This non-uniform pattern provides keys to understanding how and why metals accumulate in some places and not in others and its explanation is fundamental for mineral exploration.The most important metalliferous ore deposits are hydrothermal deposits, formed from hot waters circulating in Earth's crust. Such deposits represent a highly efficient trap where fluids were focused into a limited volume of rock, became supersaturated and precipitated ore minerals. In theory, this does not require unusual fluid compositions 1,2 as long as fluid focusing, sufficient fluid flux and efficient precipitation conditions can be maintained. Recently, this paradigm has been challenged by the recognition that ore fluids in sediment-hosted 3-5 , epithermal 6,7 and porphyryrelated [8][9][10] hydrothermal deposits can carry orders of magnitude more metal than previously considered probable, or measured in modern fluid samples. This suggests that our understanding of metal extraction and transport processes is incomplete.Here, this theme is explored by consideration of porphyry ore deposits [11][12][13][14][15] , remarkable geochemical anomalies that can contain up to 1 Gt of sulphur 16 , 200 Mt copper, 2.5 Mt molybdenum and 2600 t gold 17 . The most copper-rich examples include the 4-5 million-year old El Teniente and Rio Blanco-Los Bronces deposits in Central Chile, and the most gold-rich is the 3 million-year old Grasberg deposit in Irian Jaya, Papua New Guinea 17 .Porphyry deposits...

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Section: Volatile Exsolution and Ore Formationmentioning

confidence: 99%

Triggers for the formation of porphyry ore deposits in magmatic arcs

2013

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“…The following terms are employed in the sense of Barton et al (1963), Barton (1970), Hemley and Hunt (1992), and Einaudi et al (2003). "Mineral assemblage:" A group of minerals that occur in direct contact and display no evidence of reaction with one another (Einaudi et al, 2003).…”

Section: Terminologymentioning

confidence: 99%

“…"Mineral assemblage:" A group of minerals that occur in direct contact and display no evidence of reaction with one another (Einaudi et al, 2003). Although Hemley and Hunt (1992) applied this term when chemical equilibrium is implied, in this work the term mineral assemblage is strictly descriptive. Minerals that constitute an assemblage are joined with hyphen signs.…”

Section: Terminologymentioning

confidence: 99%

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Cordilleran Epithermal Cu-Zn-Pb-(Au-Ag) Mineralization in the Colquijirca District, Central Peru: Deposit-Scale Mineralogical Patterns

Bendezu¹,

Fontboté²

2009

Economic Geology

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Abstract0361-0128/09/3845/905-40 905 Introduction PERU is a major producer of silver, copper, zinc, lead, bismuth, tin, and gold. Of these metals, zinc, lead, silver, tin, and bismuth are produced dominantly from deposits of several styles but all sharing the following major features: (1) polymetallic (Cu-Zn-Pb-Ag-Au) suite; (2) zoned from inner Cu-bearing to outer Zn-Pb−bearing ores; (3) sulfide-rich character, commonly massive; and (4) primary occurrence as open-space fillings (veins, breccia bodies) in silicate host rocks and as replacements in carbonate rocks. Sawkins (1972) classified ores displaying these features as Cordilleran vein-type deposits. Later, Einaudi (1982) described these deposits as Cordilleran vein or lode deposits within the context of porphyry-related systems. Additional general discussions on Cordilleran vein deposits are given by Guilbert and Park (1986), Bartos (1989), andBendezú (2009). Recently, this type of mineralization has been termed "zoned base metal veins" by Einaudi et al. (2003); however, a clear zonation is not always recognized, and the ores in many districts are dominantly mantos and not veins, and they commonly contain Au and Ag in addition to base metals. We therefore prefer the more general term "Cordilleran polymetallic deposits" Fontboté and Bendezú, 2009 AbstractAt Colquijirca, central Peru, a Miocene diatreme-dome complex is associated in space and time with several large epithermal polymetallic (Cu-Zn-Pb-Au-Ag) deposits of the Cordilleran class. Of these deposits, Smelter and Colquijirca, located in the northern sector of the district, are part of a continuously mineralized northsouth corridor that extends for nearly 4 km outward from the diatreme-dome complex and to depths of 1 km below surface. This corridor is zoned from Cu-(Au) ores in its inner parts (Smelter deposit) to peripheral ZnPb-(Ag) ores (Colquijirca deposit). The Smelter-Colquijirca corridor has undergone minor erosion, providing a good example of a nearly intact paleo-epithermal system of the Cordilleran class.This description of the hypogene mineralogical patterns of the Smelter-Colquijirca corridor leads to the proposal that they are the result of superimposition in time and space of three main stages. During an early quartzpyrite stage, in which basically no economic ore deposition occurred, carbonate rocks surrounding the Marcapunta diatreme-dome complex were replaced by quartz and pyrite. This was followed by the main ore stage, which was largely superimposed on the quartz-pyrite replacements and produced zonation of ore minerals and metals along much of the Smelter-Colquijirca corridor. The zoning from Cu ores to Zn-Pb ores is complex and comprises a number of distinct and well-defined zones that display abrupt or gradual interfaces between zones. From internal to external parts, these zones consist mainly of the following mineral associations and assemblages: (1) enargite ± (luzonite, pyrite, colusite, tennantite, goldfieldite, ferberite, gold-silver tellurides, bismuthinite, gold, alunite,...

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“…For the opposite situation, in which later fluids are less acid and have lower fO2 and fs2, the evolution is defined as "retrograde." Note that this usage differs from that of Hemley and Hunt (1992), who use "prograde" and "retrograde" principally in a thermal sense. Bartos was concerned mainly with base-metal-enriched deposits, but the same ideas may have important implications in discussions of genesis of gold-silver deposits.…”

Section: Introductionmentioning

confidence: 95%

Advances in research on mineral resources, 1994

Berger¹

1994

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Cover. Part of a color shaded-relief aeromagnetic map of north-central Minnesota. Color changes represent broad changes in magnetic field strength. The warm colors (red, orange, and yellow) represent areas of magnetic field highs; the cool colors (green, blue, and purple) represent magnetic field lows.[From Horton, R.J., Day, W.C., and Bracken, R.E., Aeromagnetic survey of north-central Minnesota, chap. T of Scott, R.W., Jr., Detra, P.S., and Berger, B.R., eds., Advances Related Geographic landscapes change only slowly, but political and economic landscapes can change abruptly and unexpectedly The geological sciences are contributors to changes in these landscapes, but they also serve as a source of information on which an informed polity may base decisions on behalf of a society. The U.S. Geological Survey (USGS) is dedicated to providing information for the public good in all aspects of the geological sciences, including mineral resources.Mineral resources are a part of the geosciences that impact all aspects of a society from national economic security to national defense to land-use decisions to health and welfare these impacts affect not just humans but all other animals as well as all flora. Minerals are an essential part of the well-being of both a society and the Earth. They serve as the basis for infrastructure, technological innovation and development, economic policies, national defense, and national economic security; they are also essential to informed decisions on environmental risk and environmental tradeoffs in any decision-making process.The USGS provides mineral resource information, knowledge, and technical analyses from highly trained scientists with broad-ranging technical skills to Federal, State, and local governments; industries; schools and universities; and the general public of the United States. It also engages in cooperative studies with other countries and their institutions to provide training, exchange information and understanding, and attack important scientific problems. This Bulletin, Advances in research on mineral resources, 1994, reports progress on some of the current domestic and international research activities of the Office of Mineral Resources, Geologic Division of the USGS. ESTABLISHING A GEOLOGIC FRAMEWORK FOR MINERAL DEPOSITSSince the emergence of economic geology as a recognized subdiscipline within the earth-science research community within the last century, there has been heated debate about the role of igneous processes in the genesis of deposits that are spatially associated with intrusions and volcanic rocks. Do the metals in most deposits come from magmas, or is the magma merely a partial contributor or simply a heat engine? Even the use of sophisticated new technologies in the post-World War II era has not caused the issue to wither. Although there are stable-isotope methodologies to fingerprint probable water sources and radiogenic methodologies that reveal the source of some metals (and most deposits and rocks can now be dated with high precision), the...

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Hydrothermal ore-forming processes in the light of studies in rock-buffered systems; II, Some general geologic applications

Cited by 186 publications

References 0 publications

Triggers for the formation of porphyry ore deposits in magmatic arcs

Triggers for the formation of porphyry ore deposits in magmatic arcs

Cordilleran Epithermal Cu-Zn-Pb-(Au-Ag) Mineralization in the Colquijirca District, Central Peru: Deposit-Scale Mineralogical Patterns

Advances in research on mineral resources, 1994

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