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3. Historical Evolution of Descriptive and Genetic Knowledge and Concepts 3. Historical Evolution of Descriptive and Genetic Knowledge and Concepts By W.C. Pat Shanks III 3 of 21 Volcanogenic Massive Sulfide Occurrence Model Scientific Investigations Report 2010–5070–C U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2012 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Shanks III, W.C. Pat, 2012, Historical evolution of descriptive and genetic knowledge and concepts in volcanogenic massive sulfide occurrence model: U.S. Geological Survey Scientific Investigations Report 2010–5070 –C, chap. 3, 6 p. 25 Contents Hydrothermal Activity and Massive Sulfide Deposit Formation on the Modern Seafloor ..............27 References Cited..........................................................................................................................................31 Figures 3–1. Map of seafloor tectonic boundaries, metalliferous sediment distribution, locations of seafloor hydrothermal vents and deposits, and distribution of U.S. Exclusive Economic Zones ...............................................................................................28 3 –2. Representative examples of large seafloor massive sulfide deposits ................................30 3. Historical Evolution of Descriptive and Genetic Knowledge and Concepts By W.C. Pat Shanks III Massive sulfide deposits of base metal sulfides are among on continental hot springs (White and others, 1963), and, in the earliest metallic ore deposits known and extracted because particular, discovery of modern seafloor hydrothermal activity of their high grade, strong contrast with country rocks, iron (Miller and others 1966; Bischoff, 1969; Edmond and others, staining and gossans at the surface, and their relatively simple 1979; Hekinian and others, 1980; Spiess and others, 1980). mining and extraction. However, understanding the timing and mode of emplacement of these deposits proved much more difficult, and it was not until the second half of the twentieth Hydrothermal Activity and Massive century that several lines of evidence, not the least being the discovery of hydrothermal activity on the modern seafloor, Sulfide Deposit Formation on the conspired to convince researchers and explorationists that Modern Seafloor these deposits form syngenetically at or slightly beneath the seafloor by hydrothermal exhalative processes. The recognition of abundant and widespread hydrother- Most workers in the nineteenth century believed massive mal activity and associated unique lifeforms on the ocean sulfide deposits, including many that would later be recog- floor is one of the great scientific discoveries of the latter half nized as VMS deposits, formed by fissure-filling and (or) of the twentieth century. Studies of seafloor hydrothermal selective hydrothermal replacement. The source of the fluids processes led to advances in understanding fluid convection was controversial, with some researchers favoring lateral- and the cooling of the ocean crust, the origin of greenstones secretion from country rocks and some favoring fluids from and serpentinites, and the origin of stratiform and statabound granitoid intrusives (Stanton, 1984). Emmons (1909) studied massive sulfide deposits. Suggestions of possible submarine so-called segregated vein deposits in the Appalachians from hydrothermal activity date from the late 1950s when a number Newfoundland to Georgia and established that many of the of investigators debated the importance of “volcanic emana- deposits were formed prior to regional metamorphism. He tions” as a factor in the widespread occurrence of manganese noted the complete gradation from schistose country rock to nodules and other ferromanganese oxide deposits on the sulfide-schist laminations to massive sulfide, and concluded seafloor. For example, Arrhenius and Bonatti (1965), in their that the country rock and interbedded and massive ore are classic paper “Neptunism and Vulcanism in the Oceans,” all of the same age. Despite these seminal observations and stated the following: interpretations, most workers accepted epigenetic theories, The origin of authigenic minerals on the ocean floor and even Emmons switched to a selective-replacement theory has been extensively discussed in the past with for Ducktown ores (Emmons and Laney, 1911). The work of emphasis on two major processes: precipitation from Lindgren (1913) emphasized magmatic hydrothermal replace- solutions originating from submarine eruptions, ment theories and was very influential, especially in North and slow precipitation from sea water of dissolved America. elements, originating from weathering of continental In the 1950s, discoveries of stratiform volcanic-hosted rocks. It is concluded that in several marine authi- massive sulfides in the Bathurst area of New Brunswick genic mineral systems these processes overlap. (p. 7) opened the door for syngenetic interpretations (Stanton, 1959). These ideas coincided with the emergence of the exhalative Boström and Peterson (1966), in another classic paper, theory as applied to massive sulfide deposits of the Norwegian published evidence for extensive and widespread Fe-rich and Irish Caledonides (Oftedahl,1958; Dunham,1964). metalliferous sediments on the seafloor with a distribution Though still controversial in some quarters, the modern strongly correlated with the mid-ocean ridges (fig. 3–1). They era of studies of volcanic exhalative massive sulfides emerged stated: in the 1960s through a combination of new discoveries and On the very crest of the East Pacific Rise, in equato- new exposures, improved radiometric dating, fluid inclu- rial latitudes—particularly 12o to 16oS, the sedi- sion studies, new stable and radiogenic isotope studies, work ments are enriched in Fe, Mn, Cu, Cr, Ni, and Pb. 28 120ºE 180ºW 120ºW 60ºW 0º 60ºE 3. Historical Evolution of Descriptive and Genetic Knowledge and Concepts 60ºN ASIA MIDDLE VALLEY JUAN EUROPE ASIA DE FUCA RIDGE NORTH AMERICA LOST CITY ESCANABA TROUGH ENDEAVOUR RAINBOW 30ºN IZU-BONIN GUAYMAS TAG 21ºN ATLANTIS II DEEP RED SEA EAST Africa MARIANA MID-ATLANTIC PACIFIC 13ºN Marianas Trench HAWAII RIDGE AFRICA Marine National Monument RISE 9−10ºN Galapagos 0º MANUS BASIN Rift SOUTH FIJI fossil AMERICA CENTRAL Galapagos INDIAN LAU Rise RIDGE SOUTHERN EPR BAUER AUSTRALIA DEEP 30ºS KERMADEC PACIFIC CHILE ANTARCTIC S.W. INDIAN RISE RIDGE RIDGE 60ºS ANTARCTIC PENINSULA EXPLANATION (Al + Fe + Mn) High-temperature hydrothermal Al vents and related polymetallic sulfide deposits < 1.7 Low-temperature vent sites 1.7−2.5 and other hydrothermal 2.5−5 deposits—Including Fe-Mn 5−10 crusts and metalliferous > 10 sediments U.S. Exclusive Economic Zone Distribution of Seafloor Metalliferous Sediment, Massive Sulfide Deposits, and Hydrothermal Vents Modified after Hannington and others (2007) and Bostrom and others (1969) Figure 3–1. Map of seafloor tectonic boundaries, metalliferous sediment distribution (modified from Boström and Peterson, 1966), locations of seafloor hydrothermal vents and deposits (modified from Hannington and others, 2005), and distribution of U.S. Exclusive Economic Zones. [Al, aluminum; Fe, iron; Mn, manganese] Hydrothermal Activity and Massive Sulfide Deposit Formation on the Modern Seafloor 29 The correlation of these areas of enrichment to areas on the mid-ocean ridges (fig. 3–2), including the Trans- of high heat flow is marked. It is believed that these Atlantic Geotraverse (TAG) site on the Mid-Atlantic Ridge precipitates are caused by ascending solutions of (Humphris and others, 1995), the Middle Valley site (Zie- deep-seated origin, which are probably related to renberg and others, 1998) on the northernmost Juan de Fuca magmatic processes at depth. The Rise is consid- Ridge, and the 12o43’ N site slightly east of the East Pacific ered to be a zone of exhalation from the mantle of Rise (Fouquet and others, 1996). the earth, and these emanations could serve as the In the back-arc extensional environment of eastern original enrichment in certain ore forming processes. Manus Basin, massive sulfide deposits with high concentra- (p. 1258) tions of Cu, Zn, Au, Ag, Pb, As, Sb (antimony), and Ba (fig. 3–2) are hosted by calc-alkaline rocks ranging in composition At about the same time, the discovery of hot brine pools from basalt to rhyolite. These deposits have been sampled on the floor of the Red Sea (fig. 3–1) indicated the possibility and drilled for exploration purposes (Binns and Scott, 1993), of direct precipitation of metalliferous sediments (fig. 3–2) and high grades and significant tonnages have spurred some from hydrothermal brines on the seafloor (Miller and oth- companies to complete environmental studies, and develop ers, 1966; Bischoff, 1969, Hackett and Bischoff,
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