Lewis Ponds, a hybrid carbonate and volcanic-hosted polymetallic massive sulphide deposit, New South Wales, Australia

Abstract

The Lewis Ponds Zn-Pb-Cu-Ag-Au deposit, located in the eastern Lachlan Fold Belt, central western New South Wales, exhibits the characteristics of both volcanic-hosted massive sulphide and carbonate-hosted replacement deposits. Two stratabound massive to disseminated sulphide zones, Main and Toms, occur in a tightly folded Upper Silurian sequence of marine felsic volcanic and sedimentary rocks. They have a combined indicated resource of 5.7 Mt grading 3.5% Zn, 2.0% Pb, 0.19% Cu, 97 g/t Ag and 1.9 g/t Au. Main Zone is hosted by a thick unit of poorly sorted mixed provenance breccia, limestone-clast breccia and quartz crystal-rich sandstone, whereas Toms Zone occurs in the overlying siltstone. Pretectonic carbonate-chalcopyrite-pyrite and quartz-pyrite stringer veins occur in the footwall porphyritic dacite, south of Toms Zone. Strongly sheared dolomite-chalcopyrite-pyrrhotite veins directly underlie the Toms massive sulphide lens. The mineralized zones consist predominantly of pyrite, sphalerite and galena. Paragenetically early framboidal, dendritic and botryoidal pyrite aggregates and tabular pyrrhotite pseudomorphs of sulphate occur throughout the breccia and sandstone beds that host Main Zone, but are rarely preserved in the annealed massive sulphide in Toms Zone. Main and Toms zones are associated with a semi-conformable hydrothermal alteration envelope, characterized by texturally destructive chlorite-, dolomite-and quartz-rich assemblages. Dolomite, chlorite, quartz, calcite and sulphides have selectively replaced breccia and sandstone beds in the Main Zone host sequence, whereas the underlying porphyritic dacite is weakly sericite altered. Vuggy and Editorial handling: D. Lentz

Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen Ore District, Fennoscandian Shield, Sweden

“…A hybrid model between carbonate replacement and sub-or seafloor VMS has been suggested for the Lewis Ponds massive sulfide deposit, New South Wales, Australia. However, at Lewis Ponds, these components form separate zones and not a continuous system as at Falun (Agnew et al, 2005).…”

Hydrothermal alteration, lithogeochemical marker units and vectors towards mineralisation at the Svärdsjö Zn-Pb-Cu deposit, Bergslagen, Sweden

“…The sulphide mineralisations are stratabound to the marble units, suggesting that these acted as chemically reactive traps, causing precipitation of sulphides by increased pH, carbonate dissolution and fluid mixing Kampmann et al 2017). Similar interpretations have been made at other carbonate-hosted, volcanic-associated replacement deposits such as Garpenberg in the BLU (Allen et al 2003) and the Lewis Ponds deposit in New South Wales, Australia (Agnew et al 2005).…”

The Paleoproterozoic Aripuana Zn-Pb-Ag (Au, Cu) Volcanogenic Massive Sulfide Deposit, Mato Grosso, Brazil: Geology, Geochemistry of Alteration, Carbon and Oxygen Isotope Modeling, and Implications for Genesis

“…Published literature on volcanogenic massive sulfide deposits shows that volcanogenic deposits with large quantities of hydrothermal carbonate are uncommon, even if this mineral is usually found in minor amounts in most deposits; for example, Rosebery (Cambrian, Tasmania; Solomon and Walshe, 1979;Huston and Large, 1988;Khin Zaw and Large, 1990;Large, 1992;Orth and Hill, 1994); Mattabi (Archean, Sturgeon Lake region, Superior Province, Canada; Franklin et al,1975); the Kuroku-type deposits (Afterthought-Ingot region, Permian, East Shasta District, California, United States; Eastoe and Nelson, 1988); the various VHMS deposits of the Hokuroku district (Japan; Shikazono et al, 1998); Lewis Pond (Silurian, New South Wales, Australia; Agnew et al, 2005); Hellyer (Cambrian, Mount Read, Tasmania; Diagram showing the isotopic composition of carbonates that were formed from a CO2 -H2O fluid that outgases following a Rayleigh process. The two groups of curves represent different scenarios: one, in full, models a fluid with a CO2:H2O ratio of 2:3 in which the CO2 is released 4 times faster than the H2O; and another, dashed, models a fluid with CO2:H2O ratio of 1:4 that is outgassed under the same conditions.…”