Papers by Phillip Seccombe
Lithos, 1996
40Ar/ 39Ar dating of metamorphic biotite and alteration muscovite from the auriferous veins and h... more 40Ar/ 39Ar dating of metamorphic biotite and alteration muscovite from the auriferous veins and host rocks at the Hill End goldfield, N.S.W., Australia, has distinguished four major geological events, including the timing of gold mineralization. The earliest hydrothermal event occurred during the Middle Devonian Tabberabberan Orogeny (370-380 Ma) and resulted in the formation of quartz veins barren of Au. A second and major episode of vein emplacement occurred in the Early Carboniferous during the principal phase of metamorphism and deformation at 359-363 Ma. This was followed by Au accumulation in two stages: (1) after the major phases of quartz deposition, and (2) during and after the development of conspicuous internal vein laminations (N 357 Ma and N 343 Ma, respectively). Two sources of fluid are proposed for vein and ore formation. The first is a local metamorphic fluid characterized by s180n3,0 values of 8.9 to 12.5 per mil and SD,*, values of -87 to -90 per mil. The second is a mixed ore fluid with 6'*0 and 6D values in the range of 8'80u320 8.4 to 11 per mil and 6DnZo of -49 to -36 per mil. Progressive entry of this second fluid, sourced from trough-fill or deeper crustal rocks, is linked closely to cycles of gold precipitation at Hill End.
Miner Depos, 1993
Auriferous quartz veins in the Hill End goldfield, NSW, Australia, comprise bedding-parallel vein... more Auriferous quartz veins in the Hill End goldfield, NSW, Australia, comprise bedding-parallel vein sets and minor extension and fault-controlled veins which are hosted by a multiply deformed, Late Silurian slate-metagreywacke turbidite sequence. Fluid inclusions in quartz, either from bedding-parallel veins or from narrow, steeply N-dipping veins ('leader' veins) indicate a similar range in homogenisation temperatures (T o from 350°C to 110°C. Within this range, T a data demonstrate five groupings in the temperature intervals 350-280°C, 280-250°C, 250-190°C, 190-150°C, and 150-110°C, corresponding to a variety of primary and secondary inclusions developed during five periods of vein growth under a generally declining temperature re#rne. Inclusion fluids are characterised by a low salinity of around 0.1 to 3.6 wt % NaC1 equivalent. Laser Raman microprobe inclusion analysis indicates that gas-phase compositions relate to the paragenetic stage of the host quartx HzO(g ) and N 2 dominate in the primary inclusions from barren, Stage I quartz; CH4 and CH4 + H2Otg) are important in inclusions related to the early gold forming events (equivalent to Stages II and III quartz), but inclusions developed during the last episode of gold deposition are characterised by H2Om), CO 2rich and liquid-CO 2 bearing fluids. Precipitation of gold was aided by sulphidation reactions or phase separation in response to periods of vein opening. Late in the paragenesis, gold deposition may have been promoted by oxidation of the ore fluid.
The Canadian Mineralogist, Feb 1, 1996
Precambrian Res, 1996
Styles of sulphidic mineralisation recognised in the Olary Block, South Australia, include dissem... more Styles of sulphidic mineralisation recognised in the Olary Block, South Australia, include disseminated to massive stratiform and stratabound occurrences, as well as post-peak metamorphic vein-type mineralisation, corresponding to the range of deposit types in the adjacent Broken Hill Block. However, it is still unclear as to whether the epigenetic veins are genetically related to stratabound mineralisation in either of these two portions of the Meso-to Palaeoproterozoic Willyama Inliers.
Mineralogy and Petrology, 1992
Mineralogy and Petrology, 1989
... Geology compiled from New South Wales Geological Survey 1 : 250000 scale map sheets Bathurst ... more ... Geology compiled from New South Wales Geological Survey 1 : 250000 scale map sheets Bathurst ... however, to have spanned a considerable period of time and constraints on this ... Rough calculations based on average rock compositions and likely fluid concen-trations suggest ...
Mineralium Deposita, 1990
... K o P . E G OOP G , R , LAMBO . E GRO0 - fl / \-175 /~\L" /\ )ueen Bee o -,.I \ Fig. ...... more ... K o P . E G OOP G , R , LAMBO . E GRO0 - fl / \-175 /~\L" /\ )ueen Bee o -,.I \ Fig. ... J. Geol. Soc. Austral. 26:197-201 (1979) Baker, CJ, Schmidt, BL, Sherwin, L.: Revised stratigraphy of the Cobar-Gunderbooka area. Geol. Surv. ...
Journal of Geochemical Exploration, 2001
Short-wave infrared reflectance spectra obtained from a Portable Infrared Mineral Analyser (PIMA)... more Short-wave infrared reflectance spectra obtained from a Portable Infrared Mineral Analyser (PIMA) have been used to define alteration zones adjacent to base metal sulfide ore bodies at the Elura Mine, Cobar, Australia. The spectroscopic work identified white mica (sericite), chlorite and carbonates of hydrothermal origin in the alteration zones associated with the ore bodies. Weathering, alteration and ore zones can be discriminated by variations in the intensity and wavelength of relevant absorption features. Hydrothermal alteration is classified into four principal types, namely sericitic, silicic, chloritic and carbonate alteration. The first three types comprise overprinting hydrothermal assemblages of quartz, sericite, chlorite, ankerite, siderite, calcite and sulfides developed in strongly altered metasiltstone and slate of Early Devonian age, adjacent to the zinc–lead–silver mineralisation. An extensive zone of carbonate alteration, manifested as porphyroblasts of siderite in the host metasediments, is recognised beyond the zones of strong alteration. Spectral analysis is consistent with the mineralogical data obtained from XRD and XRF analyses and defines the limits of the alteration zones to distances of about 80m around the ore bodies. The study demonstrates the potential for spectral analysis to assist with drill hole logging and the identification of alteration zones as part of mineral exploration and development programs.
Chemical Geology, 1996
Sensitive high-resolution ion microprobe (SHRIMP) sulfur isotope data show that pyrrhotite, pyrit... more Sensitive high-resolution ion microprobe (SHRIMP) sulfur isotope data show that pyrrhotite, pyrite, galena and chalcopyrite in syntectonic auriferous quartz veins at the Hill End goldfield are characterized by two populations, with 8?3,,,,-values of -+ 7 and -O%O. These two populations are accounted for by fluid mixing involving two sources of sulfur during evolution of the vein systems. A local sulfur source and reduced fluids derived from trough-fill Siluro-Devonian sedimentary and volcanosedimentary sequences are responsible for the first two gold-bearing events., whereas a more oxidized fluid and a sulfur source from turbidites and volcanics in deeper parts of the crustal sequences appear responsible for gold deposition late in the second gold-forming event and are the dominant influences in the final gold-forming stage. For fine-grained mixtures, where mineral separation is difficult, the SHRIMP analyses are particularly useful for tracing detailed @"S variations of sulfides precipitated in different paragenetic stages.
The mid-Silurian to Middle Devonian Hill End Trough hosts significant low sulphide, orogenic gold... more The mid-Silurian to Middle Devonian Hill End Trough hosts significant low sulphide, orogenic gold deposits. The Hill End mineral system is the major system in the centre of the trough. The system extends for 17 km along strike with an 8 km zone from Hawkins Hill to Red Hill hosting the major gold mines. Gold production exceeds 21.46 t Au including 12 t Au from Hawkins Hill.
Flat, Stuart Town and Windeyer (Group 1) are all very similar and have average 34 S values close ... more Flat, Stuart Town and Windeyer (Group 1) are all very similar and have average 34 S values close to zero per mil. Near 0‰ 34 S signatures imply that sulfur was sourced from a magmatic reservoir. Furthermore, the large Wyoming One deposit has 34 S values significantly below 0‰ with the data implying that sulfur was sourced from a fractionated magmatic reservoir. Group 2 deposits include those at Mongarlowe, Murrumbateman, Napoleon Reefs, McMahons Reef and Springfield. These deposits have average 34 S values significantly above 0‰. With the exception of Springfield where sulfur was probably sourced from the Hill End Trough, Group 2 deposits are an order of magnitude smaller than Group 1 deposits.
Mineralogy and Petrology, 2008
The Hill End Trough (HET) is a deformed middle Silurian to Early Devonian sediment-dominated rift... more The Hill End Trough (HET) is a deformed middle Silurian to Early Devonian sediment-dominated rift within the northeastern Lachlan Orogen. The HET hosts the Hill End, Hargraves, Napoleon Reefs, Stuart Town and Windeyer low-sulfide orogenic gold deposits. Adjacent to the HET are the Bodangora and Gulgong gold deposits. In this study we present 91 new sulfur-and 18 new leadisotope analyses and collate a further 25 sulfur-and 32 lead-isotopes analyses from unpublished sources for these deposits. Larger gold deposits in the HET have near 0 δ 34 S‰ values indicating that sulfur in these systems was sourced from a magmatic reservoir. The dominant lead isotope signature for HET-hosted deposits reflects a crustal source however some mantle-derived lead has been introduced into the HET. Sulfur-and lead-isotopic results suggest that gold was sourced from mantle-derived magmatic units beneath the HET. The study supports earlier studies at Hill End by concluding that the majority of orogenic gold mineralisation in and adjacent to the HET formed during the Early Carboniferous period.
Australian Journal of Earth Sciences, 2004
Volcanic-hosted massive sulfide (VHMS) deposits of the eastern Lachlan Fold Belt of New South Wal... more Volcanic-hosted massive sulfide (VHMS) deposits of the eastern Lachlan Fold Belt of New South Wales represent a VHMS district of major importance. Despite the metallogenic importance of this terrane, few data have been published for sulfur isotope distribution in the deposits, with the exception of previously published studies on Captains Flat and Woodlawn (Captains Flat-Goulburn Trough) and Sunny Corner (Hill End Trough). Here is presented 105 new sulfur isotope analyses and collation of a further 92 analyses from unpublished sources on an additional 12 of the VHMS systems in the Hill End Trough. Measured ␦ 34 S values range from -7.4‰ to 38.3‰, mainly for massive and stockwork mineralisation. Sulfur isotope signatures for polymetallic sulfide mineralisation from the Lewis Ponds, Mt Bulga, Belara and Accost deposits (group 1) are all very similar and vary from -1.7‰ to 5.9‰. Ore-forming fluids for these deposits were likely to have been reducing, with sulfur derived largely from a magmatic source, either as a direct magmatic contribution accompanying felsic volcanism or indirectly through dissolution and recycling of rock sulfide in host volcanic sequences. Sulfur isotope signatures for sulfide mineralisation from the Calula, Commonwealth, Cordillera and Kempfield deposits, Peelwood mine and Sunny Corner (group 2) are similar and have average ␦ 34 S values ranging from 5.4‰ to 8.1‰.
The mid-Silurian to Middle Devonian Hill End Trough hosts significant low sulphide, orogenic gold... more The mid-Silurian to Middle Devonian Hill End Trough hosts significant low sulphide, orogenic gold deposits. The Hill End mineral system is the major system in the centre of the trough. The system extends for 17 km along strike with an 8 km zone from Hawkins Hill to Red Hill hosting the major gold mines. Gold production exceeds 21.46 t Au including 12 t Au from Hawkins Hill.
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Papers by Phillip Seccombe