All massive base metal sulphides are exhalative, and synsedimentary, but this major family of ores is divisible into two groups; one formed in volcanic and the other in sedimentary rocks. Each group includes differing varieties distinguishable by their geological characteristics. These varieties span a complete spectrum from ensimatic to ensialic geological environments and their distribution in rocks of Archean to Recent age indicates an evolutionary sequence in their development. Some varieties exhibit significant geological similarities, suggesting genetic affinities. to porphyry copper and Mississippi Valley type deposits. Broad crustal tectonic processes controlled both spatial and temporal distributions of all these deposits, which may therefore indicate the processes and evolutionary sequence of paleocrustal tectonism.
Research Article| September 01, 1993 Oxygen isotopic study of the nature and provenance of large quartz and chert clasts in gold-bearing conglomerates of South Africa and Stable isotope compositions of quartz pebbles and their fluid inclusions as tracers of sediment provenance: Implications for gold-and uranium-bearing quartz pebble conglomerates: Comment and Replies R. W. Hutchinson; R. W. Hutchinson 1Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado 80401 Search for other works by this author on: GSW Google Scholar R. P. Viljoen; R. P. Viljoen 275 Fox Street, Johannesburg 2001, South Africa Search for other works by this author on: GSW Google Scholar Torsten W. Vennemann; Torsten W. Vennemann 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Search for other works by this author on: GSW Google Scholar Stephen E. Kesler; Stephen E. Kesler 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Search for other works by this author on: GSW Google Scholar James R. O'Neil; James R. O'Neil 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Search for other works by this author on: GSW Google Scholar J. M. Barton, Jr.; J. M. Barton, Jr. 4Department of Geology, Rand Afrikaans University, P.O. Box 524, Johannesburg 2000, South Africa Search for other works by this author on: GSW Google Scholar D. B. Wenner; D. B. Wenner 5Department of Geology, University of Georgia, Athens, Georgia 30602 Search for other works by this author on: GSW Google Scholar D. K. Hallbauer D. K. Hallbauer 6Department of Geology, University of Stellenbosch, Stellenbosch 7600, South Africa Search for other works by this author on: GSW Google Scholar Author and Article Information R. W. Hutchinson 1Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado 80401 R. P. Viljoen 275 Fox Street, Johannesburg 2001, South Africa Torsten W. Vennemann 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 Stephen E. Kesler 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 James R. O'Neil 3Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109 J. M. Barton, Jr. 4Department of Geology, Rand Afrikaans University, P.O. Box 524, Johannesburg 2000, South Africa D. B. Wenner 5Department of Geology, University of Georgia, Athens, Georgia 30602 D. K. Hallbauer 6Department of Geology, University of Stellenbosch, Stellenbosch 7600, South Africa Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1993) 21 (9): 858–861. https://doi.org/10.1130/0091-7613(1993)021<0858:OISOTN>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation R. W. Hutchinson, R. P. Viljoen, Torsten W. Vennemann, Stephen E. Kesler, James R. O'Neil, J. M. Barton, D. B. Wenner, D. K. Hallbauer; Oxygen isotopic study of the nature and provenance of large quartz and chert clasts in gold-bearing conglomerates of South Africa and Stable isotope compositions of quartz pebbles and their fluid inclusions as tracers of sediment provenance: Implications for gold-and uranium-bearing quartz pebble conglomerates: Comment and Replies. Geology 1993;; 21 (9): 858–861. doi: https://doi.org/10.1130/0091-7613(1993)021<0858:OISOTN>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract No abstract available First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Meikle mine exploits one of the world’s highest grade Carlin-type gold deposits with reserves of ca. 220 t gold at an average grade of 24.7 g/t. Locally, gold grades exceed 400 g/t. Several geologic events converged at Meikle to create these spectacular gold grades. Prior to mineralization, a Devonian hydrothermal system altered the Bootstrap limestone to Fe-rich dolomite. Subsequently the rocks were brecciated by faulting and Late Jurassic intrusive activity. The resulting permeability focused flow of late Eocene Carlin-type ore fluids and allowed them to react with the Fe-rich dolomite. Fluid inclusion data and mineral assemblages indicate that these fluids were hot (ca. 220°C),of moderate salinity ( 2 S rich. Gold-rich pyrite formed by dissolution of dolomite and sulfidation of its contained Fe. Where dissolution and replacement were complete, ore-stage pyrite and other insoluble minerals were all that remained. Locally, these minerals accumulated as internal sediments in dissolution cavities to form ore with gold grades >400 g/t. Petrographic observations, geochemical data, and stable isotope results from the Meikle mine and other deposits at the Goldstrike mine place important constraints on genetic models for Meikle and other Carlin-type gold deposits on the northern Carlin trend. The ore fluids were meteoric water ( δ D = –135‰, δ 18 O = –5‰) that interacted with sedimentary rocks at a water/rock ratio of ca. 1 and temperatures of ca. 220°C. The absence of significant silicification suggests that there was little cooling of the ore fluids during mineralization. These two observations strongly suggest that ore fluids were not derived from deep sources but instead flowed parallel to isotherms. The gold was transported by H 2 S ( δ 34 S = 9‰), which was derived from Paleozoic sedimentary rocks. The presence of auriferous sedimentary exhalative mineralization in the local stratigraphic sequence raises the possibility that preexisting concentrations of gold contributed to the Carlin-type deposits. Taken together our observations suggest that meteoric water evolved to become an ore fluid by shallow circulation through previously gold- and sulfur-enriched rocks. Carlin-type gold deposits formed where these fluids encountered permeable, reactive Fe-rich rocks.
Evidence against horst and graben tectonics in the Danakil area and major separation of Danakil Alps from Ethiopian Plateau, author9s reply to discussion by Haroun Tatieff (for reference to article under discussion, see this Bibliography Vol. 32, No. 10, 02 E68-12759)
The polymetallic Madem Lakkos sulfide deposit in northern Greece is hosted within marble of the Mesozoic (?) Kerdylia Formation, a high-grade metamorphic complex composed of migmatitic biotite gneiss interlayered with marble, hornblende gneiss, and amphibolite. The Kerdylia Formation is invaded by a variety of foliated and nonfoliated intermediate to felsic intrusions of Tertiary age. The Madem Lakkos deposit is long-believed to have formed from a single epigenetic hydrothermal replacement event related to Tertiary magmatism, but this research has recognized the presence of three different and distinct ore types in the deposit that resulted from a much longer and more complex genetic history.Based on ore mineralogy, textures, and geochemistry, the Madem Lakkos ores can be characterized as (1) massive sulfide ore, (2) disseminated sulfide ore, and (3) skarn ore. The massive pyrite-sphalerite-galena ore exhibits abundant and well-developed metamorphic structures and textures that indicate the ore has been metamorphosed to upper amphibolite grade, at temperatures of at least 600 degrees C, together with its marble and gneissic host rocks. These textures include foliated-lineated galena and sphalerite, slip planes and deformation twinning in galena and sphalerite, and granoblastic annealing-recrystallization features with the development of 120 degrees triple-point junctions in galena, sphalerite, and pyrite. Despite its metamorphism, this ore preserves a generally stratiform nature with sharp, unaltered host-rock contacts, a regional and stratigraphic association with chemical and possible evaporitic metasedimentary rocks, compositional layering, and metal zoning that are consistent with formation as a sedimentary massive sulfide deposit.Disseminated sulfide ore, the most abundant type in the deposit, consists of complex veins and irregular manto-type impregnations in altered marble that are composed of pyrite, sphalerite, tennantite, chalcopyrite, arsenopyrite, galena, seligmannite, boulangerite, and minor amounts of a wide variety of additional sulfominerals in a quartz-sericite-manganiferous carbonate gangue. Disseminated sulfide ore transects and has reacted with the earlier massive sulfide ore and does not exhibit evidence of metamorphism. Euhedral zoned crystals with mineral and fluid inclusions, open-space fillings, and complex textural relationships are characteristic of this ore type and indicate that it formed through the replacement of marble by reaction with hydrothermal solutions. Disseminated sulfide ore is enriched in Cu, As, Mn, Sb, and Bi in comparison with the massive sulfide ore.Skarn ore contains pyrite, chalcopyrite, scheelite, and minor amounts sphalerite, galena, and Pb-Bi sulfominerals in a calc-silicate assemblage of gangue minerals that includes andradite-grossularite garnet, diopside, calcite, quartz, epidote, and minor chlorite, actinolite, and magnetite. Textures similar to those found in the disseminated sulfide ore and an absence of metamorphic features are characteristic of the skarn ore. Highly saline fluid inclusions in quartz from the skarn ore suggest that high-temperature, low-pressure porphyry copper-type magmatic fluids were involved in generation of this ore. Skarn ore does not exhibit a spatial relationship to igneous rocks in the mine but may be related to porphyritic quartz diorite stocks a few kilometers to the south that have halos of propylitic and phyllic alteration and porphyry copper-type mineralization.The different ore types are characterized by a very similar lead isotope composition ( 206 pb/ 204 pb = 18.78-18.82, 207 pb/ 204 pb = 15.67, 208 Pb/ 204 pb = 38.88-38.92), which lies within the restricted field of igneous rocks from northern Greece. Although this resemblance between ore and igneous rock lead has been used to support a magmatic origin for the Madem Lakkos and related sulfide deposits, the uniform isotopic composition of all lead in this tectonically active region weakens this argument. If, as is proposed, the massive sulfide ore was initially deposited as a synsedimentary body within the Kerdylia Formation, the modern model age of the lead strongly suggests that mineralization took place only a short time before the rocks were metamorphosed.The superposition of multiple ore types having different mineralogic and chemical compositions, textures, metamorphic grades, and apparent ages indicates a complex, multistage, polygenetic origin for the Madem Lakkos deposit. An interpretation consistent with this evidence is that synsedimentary massive sulfide ore was deposited as a stratiform body within a sequence of probably Mesozoic shallow-water platform carbonate and clastic-volcaniclastic sediments, possible evaporitic sediments, and lesser amounts of volcanic rocks. This ore and its host rocks were metamorphosed to upper amphibolite grade during Cretaceous-Tertiary regional metamorphism.Coregional, post-tectonic intrusions generated heat and magmatic fluids that produced skarn and skarn ore by replacement of marble at temperatures above 360 degrees C. A continuing but cooling convective hydrothermal system mixed magmatic fluids with meteoric water. These hydrothermal fluids permeated marble and massive sulfide ore peripheral to the skarn ore, reacting with them and extensively altering the marble to form disseminated sulfide ore. Massive sulfide ore and related chemical sedimentary rocks were partly dissolved by and incorporated into the hydrothermal solutions, thereby contributing Pb, Zn, Fe, Mn, Ag, Au, and minor amounts of other constituents to the hydrothermal system. Fe, Cu, W, As, Sb, and Bi were probably magmatic contributions.
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