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Tomingley - Wyoming, Caloma, Roswell, San Antonio |
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New South Wales, NSW, Australia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Tomingley gold operation includes the Wyoming 1 and Wyoming 3, and the Caloma and Caloma 2 deposits, and is located ~300 km NW of Sydney, ~40 km NNE of the Northparkes porphyry Cu-Au deposit, 52 km SW of Dubbo and ~15 km north of Peak Hill in the Lachlan Fold Belt of New South Wales, Australia (#Location: 32° 35' 22"S, 148° 13' 0"E).
Wyoming 3 is ~750 m north of Wyoming 1, while Caloma is ~500 m east of Wyoming 3, and Caloma 2 is ~500 m south of Caloma 1, and 500 m east of Wyoming 1, forming the four quadrants of a square. Mining commenced in 2014.
The Tomingley Gold Extension is to extend the life of the Tomingley Gold Operations to include the San Antonio and Roswell Resources (SAR) immediately south of the current mine. The northern margin of the combined SAR pit exploiting the upper portions of these two resources is ~2 km south of the margin of the Wyoming 1 open pit. The geology of these two resources is very similar to that at Wyoming and Caloma. The open pit will comprise three interconnecting pits encompassing the adjacent San Antonio and Roswell deposits. The total SAR pit will be up to 1.7 km long, 700 m wide and 310 m deep. The underground mine at Roswell is to utilise the exploration drive that originates from the Wyoming I underground mine.
These deposits are located near the eastern margin of the Ordovician Junee-Narromine volcanic belt of the early Palaeozoic Macquarie Arc, in the Lachlan Orogen of eastern Australia, and is close to the interpreted Parkes Thrust. The Junee-Narromine volcanic belt extends north-south for several hundred kilometres and includes the 450.9±4.2 Goonumbla Volcanic Complex which hosts the nearby Northparkes porphyry Cu-Au system. The north-south arc parallel Parkes Thrust separates the Goonumbla Volcanic Complex from the Mingelo Volcanics, a thin slice of north-south trending andesitic volcanics identified by regional aeromagnetic data and interpreted to be equivalents of the Goonumbla Volcanics. This thin volcanic belt, which hosts the Tomingley and Peak Hil gold deposits, has a strike length of ~35 km varies from 2 km in width in the north, to ~500 m in the south.
Ordovician rocks west of the Parkes Thrust are weakly deformed, with broad open folds and sub-greenschist metamorphic assemblages, while the Ordovician - Silurian sequences east of the fault, including the host Mingelo Volcanics, exhibit tight to isoclinal folding, strong axial planar cleavage with greenschist metamorphic assemblages.
The immediate Tomingley area is almost entirely covered by alluvial sequences of clays, sand and gravel of Quaternary to Cretaceous age that are up to 50 m in thickness.
The gold deposits at Tomingley are hosted within volcaniclastic sediments, rare lavas and shallow intrusive porphyritic rocks. The volcanic units are trachy-andesites to basaltic trachy-andesites, with very rare detrital quartz in the volcaniclastic rocks. The volcaniclastic rocks are dominated by well bedded sandstones and siltstones with minor breccias, lithic conglomerates and black mudstones. The sandstones and siltstones are dominant and have a primary composition of plagioclase and augite, which has been largely altered to sericite, carbonate, chlorite and albite with the rare primary quartz. These volcaniclastic rocks are intruded by numerous sill-like coarse feldspar±augite porphyritic bodies of trachy-andesitic to mafic trachy-andesite affinity which are weakly concordant to the bounding sediments. Rare peperitic textures suggest these intrusions were emplaced at a relatively shallow level.
To the west, the andesitic volcaniclastic sequence has a sharp, apparently not faulted, contact with an overlying succession of well-bedded fine quartzose sandstone and laminated siltstone with a diagnostic basal quartz rich conglomerate that may be either equivalents of the Cotton formation, part of the Goonumbla Volcanics sequence (Sherwin, 1996) or the separate Silurian Forbes Group (Squire et al., 2007). The eastern margin of the volcaniclastic sequence is uncertain.
A narrow, marginally discordant, chlorite-talc schist has also been encountered in drill core just to the east of the porphyry sills at Wyoming One, and may represent a mafic-ultramafic precursor, similar to olivine rich lavas (picrites) which are known from the Molong Belt (A Crawford, pers. comm. 2004).
The volcaniclastic sequence strikes NNW and dips steeply east, with the feldspar porphyry that hosts the Wyoming 1 deposit located near the axis of a tight, easterly vergent, antiform. Within this massive feldspar porphyry, brittle fracture is dominant and a number of vein directions are evident. Major structures are orientated WNW, as shown by the near vertical faults that appear to dislocate the porphyry and several sub-parallel vein sets within the porphyry. A pervasive set of shallow north dipping veinlets also have a WNW to ENE strike. A sinistral transpressional event is indicated by structural analysis, with a rotation of the stress field to develop the mineralised vein array seen at Wyoming 1, the structures at Wyoming 3 and the regional foliation.
Gold mineralisation at Wyoming One is distributed both around and within a sub-vertical, south plunging, feldspar±augite phyric sill. The deposit can be separated into distinct mineralised zones (Alkane Resources ASX Release, September, 2015):
i). the porphyry zone - where mineralisation is hosted by a quartz stockwork within the carapace of a sub-volcanic sill with dimensions roughly 60 x 150 m;
ii). contact zone - high grade mineralisation developed along the eastern contact of the porphyry zone;
iii). hangingwall zone - a linear zone of mineralisation situated ~30 m into the hangingwall of the 'porphyry' mineralisation and hosted within silicified and brecciated carbonaceous mudstone, and is interpreted to fold around the northern end of the porphyry;
iv). the '376' zone - and east west zone of high grade mineralisation developed at the northern contact of the porphyry, interpreted to be a bounding structure and primary fluid conduit;
v). the '831' zone - one of a number of high grade east-west structures that appear to be developed in an en echelon pattern to the south of the '376' zone; and
vi). the footwall zone - a low grade zone located in a similar stratigraphic position to the hangingwall zone but in the footwall of the porphyry.
Gold mineralisation at Wyoming One is characterised by strong quartz±carbonate (ankerite)±albite±pyrite±arsenopyrite veins within intense sericite-carbonate (ankerite)-albite-quartz-(±chlorite±pyrite±arsenopyrite) alteration of the feldspar±augite-phyric intrusion and the volcaniclastic sediments. The hangingwall zone appears stratigraphically controlled by a fine-grained carbonaceous mudstone and the '376' and '831' are high grade east west zones truncating and transecting the porphyry.
The gold mineralisation at Wyoming Three also shows a strong spatial relationship with feldspar porphyritic rocks, although pervasive alteration is limited or absent, with mineralisation hosted within structurally controlled quartz±carbonate±chlorite±pyrite±arsenopyrite veining striking about 105°.
The Wyoming deposits appear to be the result of a rheological contrast between the brittle fractured porphyry host and the ductile deformation of the surrounding volcaniclastic and metasedimentary rocks. Although the timing of alteration and mineralisation in the Wyoming deposits is uncertain, a relationship with possible early to middle Devonian deformation is considered likely (Chalmers et al., 2007).
As at 31 December 2006, published mineral resources were (Alkane Resources web site, 2007):
Measured resource - 4.835 Mt @ 2.24 g/t Au
Indicated resource - 1.025 Mt @ 2.76 g/t Au
Inferred resource - 1.270 Mt @ 4.09 g/t Au
Total resource - 7.130 Mt @ 2.70 g/t Au for 18.86 tonnes of Au.
Prior to mining in 2014, JORC compliant ore reserves and mineral resources were (Alkane Resources web site, 2016):
Measured + indicated + inferred resources
Wyoming 1 - 4.742 Mt @ 2.1 g/t Au,
Wyoming 3 - 0.649 Mt @ 1.7 g/t Au,
Caloma - 5.909 Mt @ 1.8 g/t Au,
Caloma 2 - 2.169 Mt @ 2.1 g/t Au,
TOTAL - 13.469 Mt @ 1.9 g/t Au.
Proved + probable reserves (included within the resources)
Wyoming 1 - 1.864 Mt @ 1.6 g/t Au,
Wyoming 3 - 0.389 Mt @ 1.7 g/t Au,
Caloma - 1.928 Mt @ 2.2 g/t Au,
Caloma 2 - 0.239 Mt @ 3.6 g/t Au,
Stockpiles - 0.186 Mt @ 1.9 g/t Au,
TOTAL - 4.606 Mt @ 2.0 g/t Au.
Tomingley Gold Extension
The Tomingley Gold Extension comprises the NNE-SSW aligned Roswell and San Antonio resource immediately to its SSW that together extend over a strike length of ~2 km.
The Roswell and San Antonio deposits are hosted in strongly deformed and hydrothermally altered rocks of the Ordovician Mingelo Volcanic Formation, a belt of volcanic rocks that are predominantly andesitic volcaniclastic breccias, lesser sandstone/siltstone units, lavas and black mudstones. The volcanics are unconformably overlain by pelitic silts, sandstones and debris flow conglomerates of the younger Cotton Formation. Mineralisation lies within a fault bounded section of volcanic stratigraphy that strikes at 15°. The mineralisation is primarily hosted by three 'brittle' volcanic/intrusive units, two of which are monzodioritic (plagioclase-augite and feldspar-hornblende) lavas or sills, whilst the third is a feldspar phyric andesite. All are in the same structural setting as that at the Tomingley gold deposits to the north. The plagioclase-augite monzodiorite is a medium- to coarse-grained holocrystalline intrusion that is variably altered and sheared but only carries minor mineralisation. The plagioclase-hornblende monzodiorite is 25 to 50 m thick and is regarded as a lava or subvolcanic sill and is found between the andesite and the Cotton Formation. It is a significant host to mineralisation. The andesite is a major host to mineralisation, and occurs as a single lava layer up to 80 m thick at San Antonio, but is found as multiple lava layers at Roswell. These volcanic units host structural zones generated by a competency contrast between the 'brittle' volcanics and 'ductile' volcaniclastic sedimentary rocks. Mineralisation occurs as quartz-carbonate-pyrite-arsenopyrite veins hosted in phyllic altered volcanics. These sheeted quartz veins dip steeply to the east, striking at ~10°, and are typically constrained within the volcanic units or along their contacts. The sheeted veins develop into stockworks or breccias in thicker lodes. In the main resource, 1 to >5 mineralised zones, that vary from <1 to 20 m in thickness, carrying 1 to 6.5 g/t Au, are distributed over widths of <10, up to 75 m. The mineralisation has been delineated over a strike length of >600 m, remaining open to the north and at depth. Higher grade mineralisation occurs in the southern section of Roswell, proximal to and truncated to the south by a regional NW trending structure, the Rosewood Fault. The San Antonio deposit is a continuation of the mineralised zone to the south of that fault. The Rosewood Fault is of a similar orientation to the structure that dextrally offsets the Caloma mineralisation from the Wyoming deposits. The mineralisation at the Roswell Deposit is displaced by three significant, ~4 m thick dolerite dykes that dip steeply to the NNE, striking WNW. The dolerites post-date the gold mineralisation.
The information in this summary is drawn from an Akane Resources ASX Release dated 22 May, 2022.
As at 30 June 2022, published mineral resources were (Alkane Resources and Reserve Statement FY22):
Measured + indicated + inferred resources
Open Pit (cut off 0.4g/t Au Roswell and 0.5g/t Au San Antonio)
Roswell - 6.406 Mt @ 1.68 g/t Au,
San Antonio - 7.319 @ 1.73 g/t Au,
Sub-total - 13.725 Mt @ 1.709 g/t Au.
Underground (cut off 1.6g/t Au)
Roswell - 6.141 Mt @ 2.59 g/t Au,
TOTAL Resource - 19.867 Mt @ 1.98 g/t Au for 39.3 tonnes of contained gold.
The most recent source geological information used to prepare this decription was dated: 2022.
Record last updated: 23/1/2023
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Tomingley - Wyoming 1
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Chalmers D I, Ransted T W, Kairaitis R A and Meates D G, 2007 - The Wyoming gold deposits: volcanic-hosted lode-type gold mineralisation in the eastern Lachlan Orogen, Australia : in Mineralium Deposita v42 pp 505-513
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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