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Please use this identifier to cite or link to this item: http://hdl.handle.net/1959.13/916207

Title
Sulfur- and lead-isotope signatures of selected middle Silurian to Carboniferous mineral systems of the Lachlan Orogen, eastern New South Wales - implications for metallogenesis
Author/Creator
Downes, Peter M.
Institution
University of Newcastle. Faculty of Science and Information Technology, School of Environmental and Life Sciences
Description
Research Doctorate - Doctor of Philosophy (PhD)
Description
Sulfur- and lead-isotope signatures for 64 deposits/systems located in the Central and Easternn Subprovinces of the Lachlan Orogen in eastern New South Wales were characterised in the present study. Here are presented four new ⁴⁰Ar/³⁹Ar dates, 644 new sulfur- and 105 new leadisotope analyses, plus a collation of 386 unpublished and 277 published sulfur isotope and over 560 unpublished and published lead isotope analyses for middle Silurian to Early Carboniferous mineralisation. Measured δ³⁴S values for 22 VHMS deposits range between -7.4‰ to 38.3‰. S-isotope values for Currawang East, Lewis Ponds, Mount Bulga, Belara and Accost (Group 1) range from - 1.7‰ to 5.9‰ with the ore-forming fluids for this group of deposits likely to have been reducing and sulfur derived largely from magmatic sources. By contrast, S-isotope signatures for sulfides from Black Springs, Calula, Captains Flat, Commonwealth, Cordillera, Gurrundah, Kempfield, Peelwood mine, Sunny Corner, The Glen, Wet Lagoon and Woodlawn (Group 2) have average δ³⁴S values between 5.4‰ and 8.1‰. These deposits appear to have formed from ore fluids that were more oxidising than those for Group 1 deposits, representing a mixed contribution of sulfur derived from partial reduction of seawater sulfate, in addition to sulfur from other sources. Four deposits, Elsinora, John Fardy, Mount Costigan and Stringers, have heavier average δ³⁴S signatures (10.1‰ to 13.2‰) than Group 2 deposits, suggesting that these deposits included a greater component of sulfur of seawater origin. The S-isotope data for barite from Black Springs, Commonwealth, Stringers, Gurrundah, Kempfield and Woodlawn range from 12.6‰ to 38.3‰. Over 80% of the δ³⁴S values are between 23.4‰ and 30.9‰, close to the previously published estimates for the composition of seawater sulfate during Late Silurian to earliest Devonian times, providing supporting evidence that these deposits formed concurrently with a Late Silurian volcanic event. New Pb isotope data for eleven VHMS deposits included in the present study support earlier Pb-isotope studies which indicate that lead was largely sourced from the host sequence. However, the data for Black Springs, Elsinora and Commonwealth indicate that some lead, included in these deposits, was sourced from units forming basement to the Silurian troughs. Sulfur isotope values for thirteen orogenic gold systems range between -7.5‰ and 16.1‰ (excluding outliers). The Wyoming One–Myall United system has an average δ³⁴S value of -5.5‰ and a primitive mantle-derived lead isotope signature implying that sulfur and gold were sourced from a fractionated mantle-derived intrusion. The δ-isotope data for Adelong, Bodangora, Calarie, Hargraves, Hill End, London–Victoria, Sebastopol, Sofala–Wattle Flat and Stuart Town are all very similar with average δ³⁴S values close to 0‰ (range -2.8 to 3.4‰). Sulfur in these deposits was derived from reduced fluids, sources from magmatic reservoirs either as a direct input or through dissolution and recycling of rock sulfide. For deposits hosted by the northern HET it is suggested that sulfur and gold were sourced from mantle-derived units located beneath the HET rather than the siliclastic fill of the trough itself. Windeyer and Napoleon Reefs have heavier S-isotope signatures suggesting a greater contribution of sulfur derived from reduced seawater sulfate reservoirs. Springfield, located adjacent to the northern HET, has the heaviest S-isotope signature (15.4 δ³⁴S‰) for orogenic gold deposits included in the present study. For this deposit it is suggested that HET-derived basinal fluids containing reduced seawater sulfate migrated along faults and leached gold from Ordovician mantle-derived units forming basement to that area. Seven sulfide-rich orogenic base metal deposits were included in the present study. Average δ³⁴S values for Currawang South, Frogmore, Montrose, Ruby Creek, Wallah Wallah vary between 3.5‰ and 6.0‰ (Group 1), with Kangiara, and Lucky Hit–Merrilla, having heavier average δ³⁴S values (10.0‰ and 8.2‰ respectively — Group 2). Group 1 deposits are small, and S-isotope signatures suggest significant sulfur was sourced from magmatic reservoirs; whereas, Group 2 deposits are larger and δ³⁴S signatures indicate a larger component of sulfur was derived from reduced seawater sulfate reservoirs. The Pb-isotope data for these deposits suggest that the majority of the lead was derived from older Ordovician and Silurian crustal reservoirs. The data for Mount Werong and Merrilla support a Middle Devonian Pb-model age; whereas, those for Wallah Wallah point to an Early Carboniferous Pb-model age. Browns Reef, in the Central Subprovince, is now interpreted to be a syn-deformational orogenic base metal deposit, for which the S-isotope data are similar to Group 2 orogenic base metal deposits and Pb-isotope data suggest lead was sourced from the fill of the Rast Trough. Five epithermal systems were included in the present study. Bauloora, Bowdens and those in the Yerranderie district are intermediate-sulfidation epithermal systems; whereas, Yalwal and Pambula are low sulfidation epithermal systems. Yerranderie, Yalwal, Pambula and Bauloora have δ³⁴S values close to 0‰. Sulfur in these deposits was derived largely from a magmatic reservoir. The Yerranderie system is zoned with respect to S-isotope distribution and shows mineralogical zonation along the Yerranderie Fault. Yalwal is zoned with 0‰ S-isotope values correlating with sericitic alteration assemblages and heavier S-isotope values (up to 17.9 δ³⁴S‰) correlating with assemblages that include minerals characteristic of argillic alteration. Sixteen middle Silurian to Early Devonian intrusion-related deposits were included in the present study. Collector, Dargues Reef, Mayfield, Ryans, Tallawang, Whipstick and Yambulla are located east of the I–S granite line, with Dargues Reef, Majors Creek, Mayfield, Whipstick and Yambulla hosted by or adjacent to their causative intrusion. These deposits have S-isotope signatures close to 0‰ (range -3.6‰ to 3.0‰) similar to that for granites east of the I–S line (range -1.5‰ to 4.9‰). The Pb-isotope data for these deposits includes both crustal- and mantle-derived lead. Deposits distal to their causative intrusions (Collector and Ryans) have heavier S-isotope signatures (7.7‰ and 4.3‰ respectively) indicating that some sulfur was probably sourced from the host sequence. The majority of lead, for these deposits, was sourced from the host sequence and/or older reservoirs. The S-isotope data for Tallawang suggest that the sulfur was largely sourced from the host sequence. Eight deposits are located to the west of the I–S line. Nasdaq, Phoenix, Tara, Rye Park and Mineral Hill have heavier S-isotope signatures (range: 2.6‰ to 7.3‰) which overlap with the range of values typical of granites located to the west of the I–S line (1.9 to 9.6‰) supporting the interpretation that the majority of sulfur was derived from the causative intrusion. The Pb-isotope data for Nasdaq, Mineral Hill and Tara suggest that lead originated from the host sequence or from older lead reservoirs; whereas, at Rye Park and Phoenix lead was probably sourced from the causative intrusion. Ardlethan and Browns Creek deposits have near 0‰ S-isotope signatures, lower than the range of δ³⁴S values for granites west of the I–S line which is accounted for by mantle-derived volatiles and a possible biogenic sulfur component. The Pb-isotope data for these two deposits are consistent with a lead sourced largely from the causative intrusion; although, some mantlederived lead is probably present. Red Hill has the highest S-isotope signature (13.7‰) indicating that the majority of sulfur was sourced from a seawater sulfate reservoir. ⁴⁰Ar/³⁹Ar dating showed that intrusion-related mineralisation at Tara formed at 420 ± 2 Ma; VHMS-related mineralisation at The Glen (Glen E deposit) formed at 418.2 ± 2.2 Ma; and that the Yerranderie and Bauloora intermediate sulfidation epithermal systems formed at 372.1 ± 1.9 Ma and 371 ± 13 Ma (respectively). New dating plus a review of timing constraints to Tabberabberan and Kanimblan cycle-related mineralisation highlighted metallogenic events at ~430 Ma (intrusion-related), ~420 Ma (intrusion- and VHMS-related) and a mid Devonian epithermal event. The timing of orogenic-related mineralisation is diachronous across the study area with the majority of orogenic gold systems in the west forming during the Middle Devonian Tabberabberan Orogeny; whereas, similar mineralisation in the northern HET formed during the Early Carboniferous Kanimblan Orogeny.
Relation
University of Newcastle Research Higher Degree Thesis
Date
2009
Keyword(s)
Lachlan Orogen;  Hill End Trough;  low sulfidation epithermal deposits;  intermediate sulfidation epithermal deposits;  granite-related deposits, skarns;  ⁴⁰Ar/³⁹Ar age dating;  Goulburn Trough;  Gilmore Fault Zone;  Parkes Thrust;  lead isotopes;  sulfur isotopes;  volcanic hosted massive sulfide deposits;  orogenic gold deposits;  orogenic base metal deposits
Resource Type
thesis
Rights
Copyright 2009 Peter M. Downes
Identifier
http://hdl.handle.net/1959.13/916207
Language
eng
 
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"Sulfur- and lead-isotope signatures of selected middle Silurian to Carboniferous mineral systems of the Lachlan Orogen, eastern New South Wales - implications for metallogenesis"
 
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