Volcanic-hosted Massive Sulfide Research Articles

Systematic variations in the trace element and sulphur isotope composition of pyrite with stratigraphic depth in the Skouriotissa volcanic-hosted massive sulphide deposit, Troodos ophiolite, Cyprus

The Troodos ophiolite represents one of the best-preserved fossil analogues of modern oceanic crust and includes numerous volcanic-hosted massive sulphide deposits. The actively mined Skouriotissa ...

Mineral resources of high-tech metals in Russia: State of the art and outlook

Seven main ore-forming systems—porphyry and epithermal; orogenic related to granitic intrusions; magmatic ultramafic; volcanic-hosted massive sulfide and volcanic–sedimentary; sedimentary basins; related to alkaline magmatic activity; and placers and weathering mantles—are sources of high-tech critical metals. The following promising types of ore deposits containing high-tech critical metals as by-products are recognized: Cu–Mo porphyry, Fe–Cu–Au and Pb–Zn skarn, base-metal epithermal, volcanic-hosted massive sulfide, base-metal stratiform, various tin deposits, and placers containing rare metals including REE. The mineral resources of critical metals in Russia are compared with those known in other countries. The contents of high-tech critical metals in ores of some noble-metal deposits of the Russian Northeast are reported. It is shown that the subsurface of Russia possesses considerable mineral resource potential for hightech critical metals, which allows new enterprises to be created or production of operating enterprises to increase.

Distinguishing peperite from other sediment-matrix igneous breccias: Lessons from the Iberian Pyrite Belt

Breccias composed of coarse monomictic porphyritic igneous clasts and fine-grained matrix are common in subaqueous volcanic successions. We use the descriptive name “sediment-matrix igneous breccia” for this facies and have recognized at least five different origins among examples in the Iberian Pyrite Belt: (1) peperite; (2) sediment-infill volcanic breccia; (3) mud-matrix resedimented hyaloclastite; (4) mud-rich water-settled fiamme breccia; and (5) apparent sediment-matrix igneous breccia. Because the components and textures are similar, discriminating among the different origins can be very difficult. Both peperite and sediment-infill volcanic breccia can occur along top contacts of thick intervals of felsic coherent and monomictic breccia facies. The presence of peperite indicates that the contact is intrusive, whereas the presence of sediment-infill volcanic breccia indicates that the contact is depositional. Hence, correct distinction between peperite and sediment-infill volcanic breccia is an important means of discriminating felsic intrusions from felsic lavas and domes. The distinction underpins the reconstruction of volcanic centers and facies architecture, and the ordering of volcanic, intrusive, sedimentary and mineralizing events in ancient submarine volcanic successions. In addition, in volcanic-hosted massive sulfide districts such as the Iberian Pyrite Belt, paleoseafloor positions are considered highly prospective for massive sulfide ore bodies. Correct interpretation of sediment-matrix igneous breccias is also important in this context, because sediment-infill volcanic breccia, mud-matrix resedimented hyaloclastite and mud-rich water-settled fiamme breccia all form or are deposited at the seafloor, and hence delineate paleoseafloor positions. In contrast, peperite and apparent sediment-matrix igneous breccias form subsurface and do not delineate paleoseafloor positions.

Geochemistry, geochronology, and tectonic setting of early Permian (~290 Ma) volcanic-hosted massive sulphide deposits of the Tasik Chini district, Peninsular Malaysia

ABSTRACTThe age and nature of Permian volcanism and sulphide mineralization in Malaysia are poorly understood. The Tasik Chini district is located in the Central Belt of Peninsular Malaysia and hosts the Bukit Botol and Bukit Ketaya volcanic-hosted massive sulphide (VHMS) deposits. These deposits are hosted by felsic-dominated Permian felsic volcanics that are part of a mixed volcano-sedimentary rock succession. Four mineralization zones were identified in both deposits: (1) stringer sulphide/zone; (2) massive sulphide zone; (3) barite zone; and (4) Fe-Mn and Fe-Si zones. The stringer and massive sulphides generally define the lower mineralized zones, whereas the barite, Fe-Mn, and Fe-Si layers define the stratigraphically upper mineralized zones. The main sulphide phases are pyrite, chalcopyrite, sphalerite, rare galena, and trace Sn-, Au-, and Ag-bearing minerals, with the latter two confined to the massive sulphide and barite zones. Trace and rare earth element data for the host rhyodacite-rhyolite at both deposits are consistent with formation in a volcanic arc palaeotectonic setting. In comparison, the trace element data for Triassic volcanic and intrusive rocks from the Tasik Chini area have moderate to low high field strength element (HFSE) concentrations along with transitional (Zr/Y = 4–7) to tholeiitic (Zr/Y = 2–4) affinities, but have similar magmatic arc signatures. Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) U–Pb zircon dating of rhyolites from the Bukit Botol deposit yields early Permian (286 ± 4 to 292 ± 3 Ma) ages. Similarly, the zircon U–Pb age results for Bukit Ketaya rhyolites reveal early Permian (286 ± 2 to 288 ± 4 Ma) ages. The differences in geochemical and geochronological results between the early Permian host and the later Triassic volcanic and intrusive rocks are likely due to tectonic progression from a volcanic arc environment to a collisional setting.

Systematic variations of trace element and sulfur isotope compositions in pyrite with stratigraphic depth in the Skouriotissa volcanic-hosted massive sulfide deposit, Troodos ophiolite, Cyprus

The Troodos ophiolite represents one of the best-preserved fossil analogs of modern oceanic crust and includes numerous volcanic-hosted massive sulfide deposits. The Skouriotissa deposit can be separated into a stockwork ore zone and an overlying massive sulfide lens that is covered by metalliferous sediments representing the former sulfide–seawater interface. Pyrite is the dominant sulfide mineral within these ores. The trace element composition of pyrite varies systematically with stratigraphic depth (down to ~150mbsf) probably reflecting fluid temperature variations and effects of phase separation (Co, Ni, Se, Te, Bi and Cu). Metal remobilization due to hydrothermal zone refining (Zn, Sb and Pb) and fluid-seawater mixing at the seafloor (Mo) represent further important processes controlling the pyrite chemistry. Massive sulfide-hosted sphalerite and euhedral pyrite probably formed from hot fluids (~400°C), while the occurrence of colloform pyrite indicates lower precipitation temperatures (<400°C). Similar δ18O quartz-fluid equilibration temperatures (~400°C) in the stockwork zone suggest that the Skouriotissa fluids did not cool significantly during the final 150m of fluid ascent to the seafloor. The δ34S composition of deep stockwork pyrite (−1.4‰) suggests that an isotopically light magmatic volatile phase (<0‰) was added to the hydrothermal system of Skouriotissa. During further fluid ascent about 38% of Cretaceous seawater (δ34S=18–19‰) was added leading to the precipitation of stockwork pyrite with positive δ34S values (6.1‰). In addition, the chemical and textural similarities between Skouriotissa and modern seafloor vent systems and massive sulfide deposits suggest that the Skouriotissa hydrothermal system has a modern analog.

Tectono-metallogenic systems — The place of mineral systems within tectonic evolution, with an emphasis on Australian examples

Tectono-metallogenic systems are geological systems that link geodynamic and tectonic processes with ore-forming processes. Fundamental geodynamic processes, including buoyancy-related processes, crustal/lithospheric thinning and crustal/lithospheric thickening, have occurred throughout Earth's history, but tectonic systems, which are driven by these processes, have evolved as Earth's interior has cooled. Tectonic systems are thought to have evolved from magma oceans in the Hadean through an unstable “stagnant-lid” regime in the earlier Archean into a proto-plate tectonic regime from the late Archean onwards. Modern-style plate tectonics is thought to have become dominant by the start of the Paleozoic. Mineral systems with general similarities to modern or geologically recent systems have been present episodically (or semi-continuously) through much of Earth's history, but most of Earth's present endowment of mineral wealth was formed during and after the Neoarchean, when proto- or modern-style plate tectonic systems became increasingly dominant and following major changes in the chemistry of the atmosphere and hydrosphere. Changes in the characteristics of some mineral systems, such as the volcanic-hosted massive sulphide (VHMS) system, reflect changes in tectonic style during the evolution towards the modern plate tectonic regime, but may also involve secular changes in the hydrosphere and atmosphere.Whereas tectono-metallogenic systems have evolved in general over Earth's history, specific tectono-metallogenic systems evolve over much shorter time frames. Most mineral deposits form in three general tectono-metallogenic systems: divergent systems, convergent systems, and intraplate systems. Although fundamental geodynamic processes have driven the evolution of these systems, their relative importance may change as the systems evolved. For example, buoyancy-driven (mantle convection/plumes) and crustal thinning are the dominant processes driving the early rift stage of divergent tectono-metallogenic systems, whereas buoyancy-driven processes (slab sinking) and crustal thickening are the most important processes during the subduction stage of convergent systems. Crustal thinning can also be an important process in the hinterland of subduction zones, producing back-arc basins that can host a number of mineral systems. As fundamental geodynamic processes act as drivers at some stage in virtually all tectonic systems, on their own these cannot be used to identify tectonic systems. Moreover, as mineral systems are ultimately the products of these same geodynamic drivers, individual mineral deposit types cannot be used to determine tectonic systems, although mineral deposit associations can, in some cases, be indicative of the tectono-metallogenic system.Ore deposits are the products of geological (mineral) systems that operate over a long time frame (hundreds of millions of years) and at scales up to the craton-scale. In essence, mineral systems increase the concentrations of commodities through geochemical and geophysical processes from bulk Earth levels to levels amenable to economic mining. Mineral system components include the geological (tectonic and architectural) setting, the driver(s) of mineralising processes, metal and fluid sources, fluid pathways, depositional trap, and post-depositional modifications. All of these components link back to geodynamic processes and the tectonic system. For example, crustal architecture, which controls the spatial distribution of, and fluid flow, within mineral systems, is largely determined by geodynamic processes and tectonic systems, and the timing of mineralisation, which generally is relatively short (commonly <1Myr), correlates with local and/or far-field tectonic events.The geochemical characteristics of many mineral systems are a consequence of their geodynamic and tectonic settings. Settings that are characterised by low heat flow and lack active magmatism produce low temperature fluids that are oxidised, with ore formation caused largely by redox gradients or the provision of external H2S. The characteristics of these fluids are largely governed by the rocks with which they interact, rocks that have extensively interacted with the hydrosphere and atmosphere, both environments that have been strongly oxidised since the great oxidation event in the Paleoproterozoic. In settings characterised by high heat flow and active magmatism, ore fluids tend to be higher temperature and reduced, with deposition caused by cooling, pH neutralisation, depressurisation and fluid mixing. Again, the characteristics of these fluids are governed by rocks with which they interact, in this case more reduced magmatic rocks derived from the mantle or lower crust.

Monazite geochronology and geothermobarometry in polymetamorphic host rocks of volcanic-hosted massive sulphide mineralizations in the Mesoproterozoic Areachap Terrane, South Africa

The Areachap Terrane represents the medium-to high-grade metamorphic and deformed remnants of a Mesoproterozoic (ca. 1240–1300 Ma) volcanic arc bound to the margin of the Archean Kaapvaal Craton in the east, and the polydeformed and metamorphosed Proterozoic Namaqua Province in the west. There has been protracted debate as to the exact nature, origin, age and tectonic evolution of this terrane, adjacent to an important Mesoproterozoic crustal suture between the Archean Kaapvaal Craton and the Namaqua Province, which developed during the ∼1200–1000 Ma Namaquan Orogeny. The Areachap Terrane comprises highly deformed bimodal volcanic and volcano sedimentary successions that host a number of massive sulphide base metal orebodies. Samples from three of these orebodies at different locations were analysed to determine the age and P–T conditions of metamorphism along the Areachap Terrane. Metamorphic ages were determined by electron microprobe chemical dating of monazite. Garnet- and amphibole-bearing mineral assemblages were used for geothermobarometry at the Areachap Mine, located in the northern sector of the Areachap Terrane, monazite geochronology yields evidence for two populations of Th–U–Pb-ages at 1432 ± 30 Ma – a possible protolith age – and a metamorphic age of 1153 ± 21 Ma. Kantienpan and Copperton, representing the central and southern sector of the Areachap Terrane respectively, yield monazite ages for a younger metamorphic event with U–Th–Pb-ages of 1108 ± 19 Ma and 1104 ± 17 Ma, respectively. Geothermobarometric data give a differentiated view on the metamorphic evolution of the Areachap Terrane. An arc consistent clockwise P–T evolution path and upper amphibolite-facies peak metamorphic conditions are consistent at the three locations. The Areachap site shows a short prograde development with 8.0 kbar maximum pressure at circa 700 °C maximum temperature and a subsequent retrograde metamorphism. At Kantienpan, on the other hand, maximum metamorphic conditions of 6.5 kbar at 600–650 °C are obtained, whereas at Copperton retrograde metamorphism is most distinct with maximum pressures around 8 kbar at circa 650 °C. These locally differentiated metamorphic and geochronological evolution paths in the Areachap Terrane are closely related to the Mesoproterozoic events in the adjacent Namaqua Province.

Geochronology of the DeGrussa volcanic-hosted massive sulphide deposit and associated mineralisation of the Yerrida, Bryah and Padbury Basins, Western Australia

The Palaeoproterozoic Yerrida, Bryah and Padbury Group sedimentary rocks are located on the northern margin of the Archaean Yilgarn Craton and are host to epigenetic gold (Peak Hill, Fortnum and Horseshoe), volcanic-hosted massive sulphide (VHMS; Horseshoe Lights, Red Bore and DeGrussa) and epithermal copper deposits (Thaduna). The DeGrussa Cu–Au–Ag VHMS deposit (12.4Mt @ 4.7% Cu and 1.8g/t Au) comprises four lenses and is hosted in turbiditic sedimentary rocks and basalts of the DeGrussa host sediments/Karalundi Formation, the lowest mafic volcano-sedimentary unit of the Bryah Group and crosscut by intrusive dolerite of Narracoota Formation age. Immediate wall rocks to the ore lenses are commonly altered to chlorite and talc-carbonate.A number of geochronological techniques were employed to date mineralisation in the DeGrussa deposit. These include rhenium–osmium (Re–Os) of molybdenite, Pb isotopes of galena and pyrite, and U–Pb on zircon. Re–Os geochronology of molybdenite resulted in ages of 2027±7Ma and 2011±7Ma and 2013±7Ma for mineralisation, similar to Pb–Pb model ages for galena of 2060±50Ma and 2075±50Ma. U–Pb for magmatic zircons from intrusive dolerite within the mine sequence provided ages of 1991±7Ma, 1999±7Ma and 2003±7Ma with granodiorite rocks providing ages of 2014±7Ma and 2018±9Ma. Remobilisation of DeGrussa sulphides occurred at approximately 1980Ma given Re–Os ages of pyrrhotite (1982±7Ma and 1984±8Ma) and Pb–Pb pyrite ages of 1980±30Ma.Re-examination of the Pb isotopic evolution models for this area and the Capricorn Orogen suggests that the model of Stacey and Kramers (1975) is more appropriate than Cumming and Richards (1975); using the former model leads to revised model ages as follows: Horseshoe Lights VHMS 2000±35Ma; Nathans 1820±30Ma, Peak Hill (Main pit: 1610Ma, 1620Ma, 1705Ma, and 2070±30Ma; Fiveways: 1955Ma; Mt. Pleasant: 1770Ma), Horseshoe/Cassidy 1940±30Ma, Mikhaburra 1915±30Ma, and Labouchere 1800±30Ma. These new ages coincide with major regional orogenic events – the Glenburgh from 2005 to 1960Ma, the Capricorn from 1830 to 1780Ma, the Mangaroon from 1690 to 1620Ma, and the Edmundian from 920 to 850Ma. Although orogenic events are compressional, the Yerrida/Bryah Group sedimentary rocks, along with mineralisation at the DeGrussa and Horseshoe Lights deposits, were formed in an extensional basin setting during the Glenburgh Orogeny.These new ages assist in constraining stratigraphic and mineralising events of the Palaeoproterozoic Yerrida, Bryah and Padbury Group with regional orogenic events and may provide guidance for exploration for significant gold and base metal mineralisation, not only in the Bryah, but also throughout the larger Capricorn Orogen.

Lead isotopic systematics of massive sulphide deposits in the Urals: Applications for geodynamic setting and metal sources

Lead isotopic compositions of 61 samples (55 galena, one cerussite [PbCO3] and five whole ore samples) from 16 Volcanic Hosted Massive Sulphide (VHMS) deposits in the Urals Orogeny show an isotopic range between 17.437 and 18.111 for 206Pb/204Pb; 15.484 and 15.630 for 207Pb/204Pb and 37.201 and 38.027 for 208Pb/204Pb. Lead isotopic data from VHMS deposits display a systematic increase in ratios across the Urals paleo-island arc zone, with the fore-arc having the least radiogenic lead compositions and the back-arc having the most radiogenic lead. The back arc lead model ages according to Stacey–Kramers model are close to the biostratigraphic ages of the ore-hosting volcano-sedimentary rocks (ca. 400Ma). In contrast, less radiogenic lead from the fore-arc gives Neoproterozoic (~700Ma) to Cambrian (480Ma) lead model ages with low two-stage model μ values of 8.8 (parameter μ=238U/204Pb reflects the averaged U/Pb ratio in the lead source), progressively increasing stratigraphically upwards to 9.4 in the cross-section of the ore-hosting Baymak–Buribai Formation. The range of age-corrected uranogenic lead isotopic ratios of the volcanic and sedimentary host rocks is also quite large: 206Pb/204Pb=17.25–17.96; 207Pb/204Pb=15.48–15.56, and generally matches the ores, with the exception of felsic volcanics and plagiogranite from the Karamalytash Formation being less radiogenic compare to the basaltic part of the cross-section, which would potentially imply a different source for the generation of felsic volcanics. This may be represented by older Neoproterozoic oceanic crust, as indicated by multiple Neoproterozoic ages of mafic–ultramafic massifs across the Urals. The relics of these massifs have been attributed by some workers to belong to the earlier Neoproterozoic stage of pre-Uralian ocean development. Alternative sources of lead may be Archean continental crust fragments/sediments sourced from the adjacent East-European continent, or Proterozoic sediments accumulated near the adjacent continent and presently outcropping near the western edge of Urals (Bashkirian anticlinorium). The contribution of Archean rocks/sediments to the Urals volcanic rock formation is estimated to be less than 0.1% based on Pb–Nd mixing models.The most radiogenic lead found in VHMS deposits and volcanics in the Main Uralian Fault suture zone, rifted-arc and back-arc settings, show similar isotopic compositions to those of the local Ordovician MORBs, derived from highly depleted mantle metasomatized during dehydrational partial melting of subducted slab and oceanic sediments. The metasomatism is expressed as high Δ 207Pb/204Pb values relative to the average for depleted mantle in the Northern hemisphere, and occurred during the subduction of oceanic crust and sediments under the depleted mantle wedge. A seemingly much younger episode of lead deposition with Permian lead model ages (ca. 260–280Ma) was recorded in the hanging wall of two massive sulphide deposits.

High-Precision U-Pb Zircon Chronostratigraphy of the Mount Read Volcanic Belt in Western Tasmania, Australia: Implications for VHMS Deposit Formation

Research Article| March 01, 2015 High-Precision U-Pb Zircon Chronostratigraphy of the Mount Read Volcanic Belt in Western Tasmania, Australia: Implications for VHMS Deposit Formation James K. Mortensen; James K. Mortensen † 1Pacific Centre for Isotopic and Geochemical Research, Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada V6T 1Z4 †Corresponding author: e-mail, jmortensen@eos.ubc.ca Search for other works by this author on: GSW Google Scholar J. Bruce Gemmell; J. Bruce Gemmell 2CODES ARC Centre of Excellence in Ore Deposits, Private Bag 126, University of Tasmania, Tasmania 7001, Australia Search for other works by this author on: GSW Google Scholar Andrew W. McNeill; Andrew W. McNeill 2CODES ARC Centre of Excellence in Ore Deposits, Private Bag 126, University of Tasmania, Tasmania 7001, Australia Search for other works by this author on: GSW Google Scholar Richard M. Friedman Richard M. Friedman 1Pacific Centre for Isotopic and Geochemical Research, Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, Canada V6T 1Z4 Search for other works by this author on: GSW Google Scholar Economic Geology (2015) 110 (2): 445–468. https://doi.org/10.2113/econgeo.110.2.445 Article history received: 20 Aug 2012 accepted: 19 Jun 2014 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James K. Mortensen, J. Bruce Gemmell, Andrew W. McNeill, Richard M. Friedman; High-Precision U-Pb Zircon Chronostratigraphy of the Mount Read Volcanic Belt in Western Tasmania, Australia: Implications for VHMS Deposit Formation. Economic Geology 2015;; 110 (2): 445–468. doi: https://doi.org/10.2113/econgeo.110.2.445 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 SocietyEconomic Geology Search Advanced Search Abstract The Middle Cambrian Mount Read Volcanics of western Tasmania, Australia, host several world-class volcanic-hosted massive sulfide (VHMS) deposits, representing a wide range of deposit styles. Although the deposits and their host sequences are variably deformed and locally preserve spectacular examples of primary textures and structures, rapid lateral and vertical facies changes, and faults with uncertain sense and magnitude of displacement, have made it impossible to correlate stratigraphy across the belt. Previous dating studies in the area have yielded relatively imprecise crystallization ages. We have employed the chemical abrasion isotope dilution thermal ionization mass spectroscopy (ID-TIMS) U-Pb zircon method to obtain highly precise crystallization ages for a total of 18 samples of volcanic and intrusive rock units from throughout the Mount Read Volcanics and underlying mafic-ultramafic complexes. The new data permit detailed resolution of age relationships within the belt. The study establishes an age of 516.0 ± 0.9 Ma for the McIvor Hill gabbro, which is part of a mafic-ultramafic complex interpreted to underlie the Mount Read Volcanics. Magmatism in the central Mount Read Volcanics lasted at least 12.7 m.y., from 506.8 ± 1.0 Ma for a massive dacite unit in the lower part of the Central Volcanic Complex to 496.0 ± 0.9 Ma for a welded ignimbrite in the lower Tyndall Group. Together with previous age constraints, results of the study provide a precise chronostratigraphic framework for magmatism and VHMS deposit formation within the Mount Read Volcanics. The precise age data indicate that, north of the Henty fault, magmatism occurred in three discrete pulses, at least two of which were separated by periods of sedimentation. We demonstrate that VHMS deposits in the Mount Lyell, Roseberry-Hercules, and Que-Hellyer districts, comprising the majority of the known, significant VHMS deposits in the belt, formed within a narrow time interval at ~500 ± 1 Ma, at a relatively late stage in the evolution of the belt. Some of the larger intrusions in the belt (e.g., the Bonds Range porphyry; 500.4 ± 0.8 Ma) were emplaced contemporaneously with VHMS deposit formation; however, other bodies such as the Murchison granite (497.3 ± 0.9 Ma) are younger than the deposits and are unlikely to have been involved in their genesis as has previously been suggested. These conclusions will aid explorers in targeting VHMS mineralization in the Mount Read Volcanics. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Architecture of the Neoarchaean Jaguar VHMS deposit, Western Australia: Implications for prospectivity and the presence of depositional breaks

The duration and nature of breaks in Archaean volcanosedimentary packages, recently re-evaluated in the Abitibi Greenstone Belt, has been assessed at Jaguar, an Archaean Cu–Zn-rich volcanic-hosted massive sulphide (VHMS) deposit in the Teutonic Bore volcanic complex (TBVC), the Eastern Goldfields of the Yilgarn Craton, Western Australia. The deposit is hosted by coherent volcanic facies and associated volcaniclastic facies, with minor non-volcanic facies.The hypothesis that VHMS ore lies on the intersection of volcanic centres and depositional breaks is found to be valid for the Jaguar deposit, with the site being an active volcanic complex at footwall time, with further dome development close to the final ore location at Mineralised Package time, and then reoccurring volcanic complexes (andesitic and basaltic) at several points in the hangingwall succession broadly tied into the ore position.At Jaguar the entire stratigraphic sequence faces west, with no major structural complications, making it ideal for stratigraphic analysis. The footwall evidences prolific volcanism with no intervening sedimentation. The Mineralised Package (MP) consists of intercalated dacite, breccia, conglomerate, sandstone and mudstone. The footwall volcanic rocks and the MP Dacite appear to be differentiation products from the same magma chamber. A major volcanic geochemical boundary is identified between the footwall/MP (tholeiitic to transitional affinities), and the immediate hangingwall succession (calc-alkaline). The hangingwall package includes four distinct volcanic units intercalated with mass flow deposits and graphitic argillites.VHMS mineralisation occurred across a distinct change in the geochemistry of erupted volcanic facies at a time of increased volcaniclastic sedimentation and extension. This break is comparable to Member level hiatuses seen in the Abitibi GB, i.e. the most brief of breaks, because there is no silicification of sedimentary unit-tops by silicic seawater exposure, and there is minimal development of black shales. A third time-sensitive criteria was the development of peperite on the base of Hanging Wall (HW) andesite lavas. The MP closely resembles breaks within interpreted deeper water domains of the Abitibi GB, for instance, the Deloro-Tisdale assemblage interface south of Timmins.The recognition of the change in the rate of emplacement of volcanic units and particularly the change in chemistry of volcanic rocks, are critical exploration lithologic guides to use in the absence of chemical sediment deposits (exhalites). Although crustal extension and basin subsidence were factors in the shaping of the succession, their effects were too subtle to use as an exploration tool. A corollary of the recognition of a Member-level VHMS-bearing interval in the Teutonic Bore volcanic complex is that, like the Kidd-Munro assemblage stratigraphy (Abitibi GB), where several ore-bearing depositional breaks are known below the great Kidd Creek deposit, there is scope for the discovery of further (potentially larger) deposits on higher Formation or Group-level breaks in the TBVC.

Constraints on Water Depth of Massive Sulfide Formation: Evidence from Modern Seafloor Hydrothermal Systems in Arc-Related Settings

The results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation. Available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment. The shallowest hydrothermal systems in subduction-related settings are hosted by arc volcanoes. These shallow vent sites have a number of features in common with subaerial epithermal systems. Massive sulfide occurrences in arc-related rifts, the most likely setting for many ancient analogs, are generally restricted to water depths from ~700 to 2,000 m, with rifts developing within old arc crust at the deeper end of this range. Back-arc spreading centers proximal to arcs host massive sulfide deposits at depths of ~1,500 to 2,000 m. The deepest hydrothermal systems occur along mature back-arc spreading centers distal to volcanic arcs where water depths range from ~2,000 to 3,700 m. These deeper vent sites probably represent the best modern analogues of ophiolite-hosted massive sulfide deposits. Boiling of the hydrothermal fluids is common at volcanic arcs and in arc-related rifts. In these environments, elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss. By contrast, the high ambient pressures in deep marine hydrothermal systems along mature back-arc spreading centers prevent fluids from boiling during their ascent to the seafloor. Boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and, therefore, influences the metal content of seafloor sulfide deposits. Copper-rich massive sulfides typically occur at water depths exceeding ~1,000 m, whereas Zn- and Pb-rich occurrences may form at any water depth. Boiling can be an important control on Ag and Au grades but is not the only factor controlling precious metal enrichment in massive sulfides. Shallow marine hot spring deposits can be highly enriched in trace metals such as As, Hg, and Sb. Submarine volcanic arc and back-arc settings are geologically complex and significant variations in water depth can occur over short distances. Paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth. The relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic-hosted massive sulfide deposits.

Effects of temperature, sulfur, and oxygen fugacity on the composition of sphalerite from submarine hydrothermal vents

Experimental studies have shown that temperature, pressure, sulfur fugacity (fS2), and oxygen fugacity (fO2) influence the Fe content of sphalerite. We present compositional in situ data on sphalerite from submarine volcanic-hosted massive sulfide (VHMS) ores of hydrothermal vents from different plate tectonic settings and with variable host-rock compositions. Sphalerite from sediment-hosted vents has systematically higher S contents and Fe/Zn ratios than those of the sediment-starved vents, reflecting an influence of fS2 and fO2 on Fe partitioning between fluid and sphalerite. The Fe/Zn ratios of sphalerite from sediment-starved vent systems apparently increase systematically with the fluid temperatures of the corresponding vents. We conclude that the composition of sphalerite can be used to (1) distinguish between sediment-hosted and sediment-starved hydrothermal processes, and (2) estimate minimum fluid temperatures of sphalerite precipitation from inactive sediment-starved hydrothermal vent sites and fossil VHMS deposits.

Geochemistry and nano-structure of a putative ∼3240 million-year-old black smoker biota, Sulphur Springs Group, Western Australia

Filaments of pyrite found within a volcanic hosted massive sulphide (VHMS) deposit from the ∼3270–3230Ma Sulphur Springs Group of Western Australia have previously been interpreted as remnants of some of Earth's oldest thermophilic microbial communities. We here re-examine these pyrite filaments using a suite of in situ high spatial resolution techniques and provide new observations on their geochemistry, morphology, texture, distribution and habitat.A number of the Sulphur Springs filaments retain geochemical evidence for remnants of organic material. This takes the form of patches of carbon and nitrogen enrichment seemingly enclosed within a completely pyritised filament. The distribution of this organic material closely resembles that observed in younger bona fide pyritised filamentous microbes. Most filaments also possess a distinctive sponge-like nano-porous pyrite texture, which is replicated in younger pyritised microfossils and bio-mediated pyrite framboids, and is consistent with pyrite nucleation in an organic matrix. New 3D analyses confirm previous observations of approximately uniform filament diameters, lack of branching, clustering of filaments, plus zones of filaments with preferred orientations. Multiple sulphur isotope analyses indicate that the sulphur for pyritisation likely came from a mixture of seawater and magmatic sources, consistent with a black smoker type habitat and permissive of the presence of life in this setting.While these data are consistent with a biological interpretation for the Sulphur Springs filaments, perhaps as pyritised filamentous microorganisms or bundles of pyritised extra-cellular polymeric substances (EPS), the evidence is not compelling. Solid filament cross-sections and straight lengthwise morphology of most filaments resemble abiotic crystal needles or whiskers, while the parallel and radial alignments of filaments could be replicated by crystal growth patterns. Carbon and nitrogen enrichment could have occurred when organic material entrained within hydrothermal fluids was adsorbed onto these mineral crystals. Further work to obtain larger databases of nano-scale textures and morphologies from both biological and abiotic pyrite is needed before an abiotic formation mechanism can be confidently rejected.

Sulfidation of native gold

We use microscopic and electron microprobe techniques to study samples of ores containing native gold with dark rims of Au-Ag sulfides from six deposits and ore occurrences of Russia: Khopto (Au-Cu-skarn), Ulakhan, Yunoe (Au-Ag epithermal), Dorozhnoe, Konechnoe, and Yakutskoe (Au-quartz). Dark rims around native gold are uytenbogaardtite (Ag 3 AuS 2 ) or petrovskaite (AgAuS), or a mixture of acanthite (Ag 2 S) with uytenbogaardtite or uytenbogaardtite with petrovskaite. In the ore samples from the Khopto and Ulakhan deposits, we have found microrims of higher fineness gold at the contact of native gold and Au-Ag sulfide. The reactions of native gold sulfidation occurring in natural processes are proposed based on the compositions of Au-Ag sulfides, their mutual textural relationships. The composition of Au-Ag sulfides rims was found to depend on the primary fineness of native Au: uytenbogaardtite forms after gold of fineness above 380‰, whereas petrovskaite, above 650‰. We propose that the fineness of gold and silver may be used for forecasting presence of uytenbogaardtite or petrovskaite, or a mixture of acanthite with uytenbogaardtite or uytenbogaardtite with petrovskaite in sulfide ores at Au-Ag epithermal, Au-skarn, Au-Cu volcanic-hosted massive sulfide, Au-quartz-sulfide, and other deposits.

40Ar/39Ar ages and stable isotopes of supergene jarosite from the Baiyin VHMS ore field, NE Tibetan Plateau with paleoclimatic implications

Supergene jarosite is widely distributed in weathering profiles derived from hypogene sulfide ores. Precise 40Ar/39Ar dating and determination of hydrogen and oxygen isotopes of supergene jarosite can not only place tight constraints on the timing and history of continental weathering and supergene enrichment of sulfide ore deposits, but also shed significant insights into paleoclimatic conditions and tectonic uplift responsible for the weathering. In this paper, we present a preliminary study of 40Ar/39Ar geochronology and stable isotope geochemistry of supergene jarosite from the early Paleozoic Zheyaoshan volcanic-hosted massive sulfide deposit of the Baiyin ore field located in the eastern portion of the Qilian Mountain along the northeastern (NE) margin of the Tibetan Plateau in an attempt to better understand the climatic conditions prevailed during the pervasive weathering in the region. Jarosite from the Zheyaoshan mining area occurs either as gravels within alluvial deposits over low-relief flat-top hills or cm-wide veins crosscutting weathered sulfide ores or their wall rocks. The gravels consist of massive jarosite aggregates with tabular crystal morphology and contain 8.21 wt%–8.31 wt% K2O on average. Two jarosite grains extracted from the gravels (08-02-2 and 08-02-5) yield well-defined 40Ar/39Ar plateau ages of 37.1 ± 0.3 and 41.2 ± 0.4 Ma (2σ), respectively. They have δD values of −133 ‰ and −156 ‰, and \({\delta ^{18}}{{\rm{O}}_{{\rm{S}}{{\rm{O}}_4}}}\) values of 2.6 ‰ and 2.5 ‰. The vein-type jarosite consists of hexagonal pyramid crystals and contains much lower K2O, averaging at 2.44 wt%–2.72 wt%. Two jarosite veins (06-16-3 and 06-16-4) yield similar plateau ages of 3.2 ± 0.1 and 3.3 ± 0.1 Ma (2σ), respectively. These jarosite veins have δD values of −158 ‰ and −160 ‰, and \({\delta ^{18}}{{\rm{O}}_{{\rm{S}}{{\rm{O}}_4}}}\) values of 2.8 ‰ and 2.5 ‰. The 40Ar/39Ar ages indicate that sulfide ores of the Zheyaoshan deposit must have been brought to the surface since the late Eocene, and subsequently subjected to prolonged oxidation and supergene enrichment. The precipitation and preservation of jarosite in weathering profiles indicate that arid–semiarid climatic conditions must have been prevailed since the late Eocene. The hydrogen and oxygen isotopes of the jarosite further point to variation of climatic conditions in the area, with the Pliocene being slightly cooler relative to the late Eocene. Given that weathering profiles overlying sulfide ore deposits are widely distributed along the Qilian Mountain, systematic studies of 40Ar/39Ar geochronology and stable isotope geochemistry of jarosite-group minerals from these profiles would provide valuable information on the timing and evolution of regional tectonic uplift, paleoclimatic changes, and supergene mineralization in this mountainous belt along the NE edge of the Tibetan Plateau.

Lithology and mineralisation types of the Rockliden Zn–Cu massive sulphide deposit, north-central Sweden: Implications for ore processing

The Rockliden Zn–Cu volcanic-hosted massive sulphide deposit is located approximately 150 km south of the Skellefte ore district, north-central Sweden. Most of the mineralisation is found at the altered stratigraphic top of the felsic volcanic rocks, which are intercalated in the metamorphosed siliciclastic sedimentary rocks of the Bothnian Basin. Mafic dykes cross-cut all lithological units, including the massive sulphides, at the Rockliden deposit. The relatively high Sb grade of some parts of the mineralisation results in challenges in handling of the Cu–Pb concentrate in the smelting process. The aim of this study is to characterise different host rock units and ore types by their main mineralogy, as well as by their trace mineralogy with focus on the Sb-bearing minerals. Ore types are distinguished largely on the basis of their main base-metal bearing sulphide minerals, which are chalcopyrite and sphalerite. Several Sb-bearing minerals are documented and differences in the trace mineralogy between rock and ore types are highlighted. Based on the qualitative ore characterisation, rock- and ore-intrinsic parameters, such as the pyrite, pyrrhotite and magnetite content of the massive sulphides, the trace mineralogy and its association with base-metal sulphide minerals, are outlined and discussed in terms of relevance to the ore processing.

Integrated stratigraphic–structural–hydrothermal alteration and mineralisation model for the Kangaroo Caves zinc–copper deposit, Western Australia

The Kangaroo Caves volcanic-hosted massive sulfide deposit is located in the Archean Panorama district in the northern Pilbara Craton, Western Australia. The deposit contains an indicated and inferred mineral resource of 6.3 Mt at 3.3% Zn, 0.5% Cu and 12.1 g/t Ag. The Kangaroo Caves area is characterised by predominantly tholeiitic volcanic rocks of the ca 3240 Ma Kangaroo Caves Formation, which is overlain by turbiditic sedimentary and volcanic rocks of the Soanesville Group. Zinc–copper mineralisation is hosted mainly by the regionally extensive Marker Chert, the uppermost unit of the Kangaroo Caves Formation, and structurally controlled by D1 synvolcanic faults. The upper area of the deposit is characterised by quartz–sphalerite ± pyrite ± barite ± chalcopyrite, whereas the lower area contains mainly chlorite–pyrite–quartz–carbonate–sericite ± chalcopyrite ± sphalerite.Laser-ablation inductively coupled-plasma mass-spectrometry analyses show that pyrite in the Marker Chert is enriched in Zn, Ag, Pb and Sb when compared with dacite from the Kangaroo Caves Formation, Paddy Market Formation, and Dalton Suite. Pyrite from the Marker Chert also displays a negative correlation between Zn and As, i.e. with increasing Zn levels As is decreasing. The Co/Ni ratios in pyrite are significantly greater in the upper, Zn-rich area (median ratio = 0.4) of the deposit than the lower, Zn-poor area (median ratio = 5). Copper is low irrespective of the host rocks. Sphalerite displays low Fe (<10 000 ppm), Cu (<100 ppm), Ag (58 ppm) but high Cd (<500–1000 ppm). Some elevated Cu values suggest the presence of chalcopyrite inclusions, whereas elevated Cu and Sb values suggest tetrahedrite–tennantite inclusions.Structural analysis of the Kangaroo Caves area, combined with three-dimensional modelling of ore element distribution, shows that the deposit is predominantly an elongate pipe of Zn mineralisation, which plunges ~30° to the northeast and is approximately 1000 m in length. The morphology of the Kangaroo Caves deposit was largely retained from its original formation, despite rotation of the host rocks and deposit during the D2 event. Variations in hydrothermal alteration assemblages, including the Co and Ni contents of pyrite within the deposit and underlying dacite, are interpreted to be the result of variations in the influx and mixing of seawater with upwelling volcanogenic fluids during Zn–Cu mineralisation. In the Kangaroo Caves area, the Co/Ni of pyrite can be used as an exploration vector towards high-grade Zn–Cu mineralisation.

Mapping geology and volcanic-hosted massive sulfide alteration in the Hellyer–Mt Charter region, Tasmania, using Random Forests™ and Self-Organising Maps

The Hellyer–Mt Charter region of western Tasmania includes three known and economically significant volcanic-hosted massive sulfide (VHMS) deposits. Thick vegetation and poor outcrop present a considerable challenge to ongoing detailed geological field mapping in this area. Numerous geophysical and soil geochemical datasets covering the Hellyer–Mt Charter region have been collected in recent years. These data provide a rich source of geological information that can assist in defining the spatial distribution of lithologies. The integration and analysis of many layers of data in order to derive meaningful geological interpretations is a non-trivial task; however, machine learning algorithms such as Random Forests and Self-Organising Maps offer geologists methods for indentifying patterns in high-dimensional (many layered) data. In this study, we validate an interpreted geological map of the Hellyer–Mt Charter region by employing Random Forests™ to classify geophysical and geochemical data into 21 discrete lithological units. Our comparison of Random Forests supervised classification predictions to the interpreted geological map highlights the efficacy of this algorithm to map complex geological terranes. Furthermore, Random Forests identifies new geological details regarding the spatial distributions of key lithologies within the economically important Que-Hellyer Volcanics (QHV). We then infer distinct but spatially contiguous sub-classes within footwall and hangingwall, basalts and andesites of the QHV using Self-Organising Maps, an unsupervised clustering algorithm. Insight into compositional variability within volcanic units is gained by visualising the spatial distributions of sub-classes and associated statistical distributions of key geochemical data. Compositional differences in volcanic units are interpreted to reflect contrasting primary composition and VHMS alteration styles. We conclude that combining supervised and unsupervised machine-learning algorithms provides a widely applicable, robust means, of analysing complex and disparate data for machine-assisted geological mapping in challenging terranes.

Tectonic Controls on the Endowment of Neoarchean Cratons in Volcanic-Hosted Massive Sulfide Deposits: Evidence from Lead and Neodymium Isotopes

Review and analysis of initial lead isotope ratios from Archean volcanic-hosted massive sulfide (VHMS) and lode gold deposits and of neodymium isotopes from igneous rocks from the geologic provinces that host these deposits identifies systematic spatial and temporal patterns, both within and between the provinces. The Abitibi-Wawa subprovince of the Superior province is characterized by highly juvenile lead and neodymium. Most other Archean provinces, however, are characterized by more evolved isotopes, although domains within them can be characterized by juvenile isotope ratios. The analysis indicates that the endowment (measured as the quantity of metal contained in geologic resources per unit surface area) of VHMS and komatiite-associated nickel sulfide deposits is related to the isotopic character and, therefore, the tectonic history of provinces that host these deposits. Provinces with extensive juvenile crust have significantly higher endowment of VHMS deposits, possibly as a consequence of higher heat flow and extension-related faults. Provinces with evolved crust have higher endowment of komatiite-associated nickel sulfide deposits, possibly because such crust provided either a source of sulfur or a stable substrate for komatiite emplacement. In any case, initial radiogenic isotope ratios can be useful in predicting the endowment of Archean terranes for VHMS and komatiite-associated nickel sulfide deposits. Limited data suggest similar relationships may hold in younger terranes. Lead isotope data may provide constraints on supercraton reconstructions in the Archean as lead isotope systematics appear to be highly provincial. Similar isotope systematics between the Superior province and the Eastern Goldfields superterrane may indicate a linkage during the Neoarchean, consistent with the similar geologic and metallogenic histories of these provinces.