Research on hydrogeochemistry for mineral exploration for inland Australia includes development of weathering models and extensive mine-scale and regional groundwater data. Mineral saturation indices for groundwater, activity–activity plots and reaction modelling simulate weathering of volcanic-hosted massive sulfide (VHMS) deposits in deeply weathered environments. At 10 m or more below surface, dissolved O2 is very low and other solutes such as sulfate, carbonate and nitrate are more likely oxidants. Modelling indicates that these processes differ from oxic weathering of highly eroded terrains, and provide the framework to develop robust hydrogeochemical exploration procedures in covered terrains. Sulfide weathering potentially occurs in two or more phases that effect surrounding groundwaters in differing manners. Deeper oxidative alteration of sulfides (e.g. bornite to chalcopyrite), occurring tens to hundreds of metres below surface, uses sulfate and carbonate as oxidants, causing neutral to alkaline conditions. In this zone, only pyritic massive sulfides potentially generate acidic conditions. Thus, deep sulfide-rich rocks are indicated by sulfate-depleted groundwater. Closer to the surface, sulfides are oxidised to soluble sulfates by dissolved nitrate, with much less acid production than if dissolved oxygen was the main oxidant. Thus, in shallow groundwater, sulfides are indicated by sulfate enrichment and nitrate depletion. Elements are released from sulfides and wall rocks by acid or alkaline conditions. The derived FeS (pH–Eh + Fe + Mn) and AcidS (Li + Mo + Ba + Al) indices distinguish sulfide systems through tens of metres of cover. VHMS systems are distinguished from other non-economic sulfide deposits where there is little transported cover, using various dissolved elements, including Zn, Pb and Cu. Elsewhere, 'patchiness' and limited aerial extent of metal signals are due to adsorption effects, that intensify with depth. Other elements such as Mn and Co have lesser diminution effects, but are less selective indicators for VHMS. There is exploration potential for elements such as Pt or Ag. These varying sulfide indicators have moderate utility, even for large-scale (∼5 km spacing) sampling. Results indicate that hydrogeochemistry can add value to greenfields exploration for VHMS ore deposits in deeply weathered terrains. It is also moderately successful at indicating the presence of sulfide-rich systems (whether magmatic or hydrothermal) under >100 m cover, thus providing a rapid and cost-effective regional prospectivity tool for deeply buried terrains. Such mineral exploration tools will encourage exploration investment for more difficult regions of Australia and in other deeply weathered regions of the world.
Research Article| September 01, 2003 Contrasting evolution of hydrothermal fluids in the PACMANUS system, Manus Basin: The Sr and S isotope evidence S. Roberts; S. Roberts 1School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar W. Bach; W. Bach 2Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar R.A. Binns; R.A. Binns 3Commonwealth Scientific and Industrial Research Organisation Exploration and Mining, P.O. Box 136, North Ryde, NSW 1670, Australia Search for other works by this author on: GSW Google Scholar D.A. Vanko; D.A. Vanko 4Department of Physics, Astronomy and Geosciences, Towson University, Towson, Maryland 21252, USA Search for other works by this author on: GSW Google Scholar C.J. Yeats; C.J. Yeats 5Commonwealth Scientific and Industrial Research Organisation Exploration and Mining, P.O. Box 136, North Ryde, NSW 1670, Australia Search for other works by this author on: GSW Google Scholar D.A.H. Teagle; D.A.H. Teagle 6School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar K. Blacklock; K. Blacklock 7Commonwealth Scientific and Industrial Research Organisation Petroleum Resources, P.O. Box 136, North Ryde, NSW 1670, Australia Search for other works by this author on: GSW Google Scholar J.S. Blusztajn; J.S. Blusztajn 8Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar A.J. Boyce; A.J. Boyce 9Scottish Universities Environmental Research Centre, Rankine Avenue, East Kilbride G70 0QF, UK Search for other works by this author on: GSW Google Scholar M.J. Cooper; M.J. Cooper 10School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar N. Holland; N. Holland 10School of Ocean and Earth Science, Southampton Oceanography Centre, University of Southampton, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar B. McDonald B. McDonald 11Commonwealth Scientific and Industrial Research Organisation Exploration and Mining, P.O. Box 136, North Ryde, NSW 1670, Australia Search for other works by this author on: GSW Google Scholar Geology (2003) 31 (9): 805–808. https://doi.org/10.1130/G19716.1 Article history received: 02 Apr 2003 rev-recd: 05 May 2003 accepted: 11 May 2003 first online: 02 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 S. Roberts, W. Bach, R.A. Binns, D.A. Vanko, C.J. Yeats, D.A.H. Teagle, K. Blacklock, J.S. Blusztajn, A.J. Boyce, M.J. Cooper, N. Holland, B. McDonald; Contrasting evolution of hydrothermal fluids in the PACMANUS system, Manus Basin: The Sr and S isotope evidence. Geology 2003;; 31 (9): 805–808. doi: https://doi.org/10.1130/G19716.1 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 Ocean Drilling Program (ODP) Leg 193 investigated two sites of hydrothermal activity along the crest of the Pual Ridge in the eastern Manus Basin. A site of low-temperature diffuse venting, Snowcap (Site 1188), and a high-temperature black smoker site, Roman Ruins (Site 1189), were drilled to depths of 386 and 206 m below seafloor (mbsf), respectively. Although the two sites are <1000 m apart, the 87Sr/86Sr and δ34S signatures of anhydrite recovered at both sites are very different. The data suggest a complex interplay among hydrothermal fluid, magmatic fluid, and seawater during alteration and mineralization of the PACMANUS (Papua New Guinea–Australia–Canada–Manus) system. These new results significantly expand the subsurface data on seafloor hydrothermal systems and may begin to explain the earliest processes of multistage mineralization and alteration history that typify ancient massive sulfide systems. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The currently accepted model for the Archean lode gold deposits of the Yilgarn craton postulates that they represent a coherent group of epigenetic deposits, the majority of which formed during a craton-scale, broadly synchronous hydrothermal event late in the tectonothermal evolution of the granite-greenstone terranes at ca. 2640 to 2630 Ma.Felsic rocks from the southern Eastern Goldfields, which host or are cut by gold mineralization, have SHRIMP II U-Pb zircon ages of 2673 + or - 3 Ma at Mount Charlotte, 2669 + or - 17 Ma at Mount Percy, 2663 + or - 3 Ma at Racetrack, and 2657 + or - 8 Ma at Porphyry. All these ages are consistent with gold mineralization at ca. 2640 to 2630 Ma.Intermediate to felsic dikes cut typical syn- to postmetamorphic lode gold mineralization at the Mount McClure and Jundee deposits in the Yandal greenstone belt in the north of the Kurnalpi terrane. The dikes give ages of 2656 + or - 4, 2663 + or - 4, and 2668 + or - 10 Ma from Mount McClure, and 2656 + or - 7 Ma from Jundee, requiring that mineralization and peak regional metamorphism in the belt occurred prior to ca. 2660 Ma. However, both the characteristics of the Jundee and Mount McClure deposits and the relative timing of mineralization with respect to the metamorphic and structural history of the belt are similar to that seen for gold deposits elsewhere in the Yilgarn craton. This implies that mineralization at Jundee and Mount McClure was produced prior to 2660 Ma by similar processes to those seen elsewhere in the Yilgarn at 2640 to 2630 Ma.Peak metamorphism in the western, higher metamorphic grade terranes of the Yilgarn was not reached until ca. 2630 Ma, some 10 to 30 m.y. after peak metamorphism in the Kalgoorlie terrane and more than 30 m.y. after metamorphism in the Yandal belt. In addition, almost all of the published robust ages supporting gold mineralization at ca. 2640 to 2630 Ma are from the west of the craton. Consideration of the new data from the Yandal belt in conjunction with previously published geochronology throws doubt on the hypothesis that lode gold mineralization occurred approximately synchronously across the Yilgarn craton. Rather, it suggests that mineralization, along with regional metamorphism, is earlier by at least 30 m.y. in the northeastern Yilgarn craton.
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