Balcooma, Dry River South, Surveyor
Queensland, Qld, Australia
Cu Zn Pb Ag Au
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The Dry River group of volcanic hosted massive sulphide deposits, which include Balcooma, Surveyor and Dry River South are located 40 km NNW of Greenvale in north Queensland, Australia. The three deposits are distributed over a NNE trending, 4 km strike interval.
The deposits are within a NNE trending 8 x 40 km belt of strongly deformed and metamorphosed Cambrian-Ordovician volcanics and sediments, the Balcooma Metamorphics. The northern part of the belt, where the deposits are found, has been metamorphosed to middle amphibolite facies and is separated from the Mesoproterozoic Einasleigh Metamorphics by the Balcooma Mylonite. To the east, the Balcooma metamorphics are intruded by the Silurian Dido granodiorite.
The local stratigraphy comprises, from the base:
* Clayhole Creek Beds - metagreywacke with minor interbedded metapelites and metavolcanics, which in part interfingers with the overlying,
* Dry Creek Volcanics - massive quartz-feldspar porphyry, volcaniclastics and metasediments,
* West Branch Creek Beds - felsic metatuffs, metasandstones and shales, with isolated pods of the Golden Creek Volcanics,
* Lochlea Volcanics - dacitic volcaniclastics and volcanics,
* Highway Beds - interbedded metatuffs and metavolcanics.
All of these are intruded by the Cambro-Ordovician Ringwood Park Microgranite in the north-central portion of the belt.
The Balcooma deposit is hosted by a meta-pelite lens within the Clayhole Creek Beds, which has been divided into a lower and upper greywacke, separated by the metapelite which comprises two varieties of staurolite bearing schist with a number if intercalated volcaniclastic lenses. Five separate massive sulphide lenses are outlined. Two of these contain the main Cu resource, while two others are more Zn-Pb rich and the fifth has been largely eroded and weathered to now be represented as a high lead enriched gossan. These five lenses are interpretted to represent three stratigraphic levels. Two types of alteration are recognised, namely i). Quartz-chlorite schists associated with the Cu mineralisation - commonly pyrite and magnetite bearing, with a pipe like morphology, and ii). Pyritic quartz-muscovite ±biotite schists accompanying the polymetallic ores - this zone is generally stratabound.
Dry River South is a thin (1 to 10 m thick), north-south trending tabular body, 1 km long and up to 200 m wide occurring at the contact between metagreywacke and an underlying pyritic quartz-muscovite-biotite schist, near or at the contact of the Clayhole Creek Beds and the overlying Dry River Volcanics. The prospect area also contains two bodies of quartz-feldspar porphyry which are apophyses of a larger body to the west. Two types of massive sulphide are described, namely i). pyrite-chalcopyrite, and ii). pyrite-sphalerite-galena. Both are normally present in the same drillhole. The massive sulphide body is capped by a thin (<2 m thick) band of felsic volcanics. The immediate footwall comprises pyritic, fine grained quartz-muscovite schist with up to 3% biotite, scattered staurolite and rare andalusite porphyroblasts. The pyrite occurs as stingers to thick massive sulphide veins up to 40 cm thick, and as lesser disseminations. This alteration persists laterally for up to 50 m beyond the massive sulphides, but is over 100 m thick
Surveyor is a small high grade massive, stringer and disseminated sulphide deposit between Balcooma and Dry River South, in a similar setting. The deposit is bounded to the east by the Ringwood Park Microgranite which is in probable fault contact with meta-greywacke of the Clayhole Creek beds, while to the west the host rocks are in partial fault contact with quartz-feldspar porhyries of the Dry River volcanics. The deposit has been folded into a synform that plunges 20°S over a strike length of 250 m, width of 80 m and maximum true thickness of 23 m. The smaller oxide-supergene Surveyor East lens is located 200 m to the east, interpreted to be a fault offset of the main deposit across the NE trending Andesite Fault. Massive sulphide mineralisation is located at the top of the felsic Dry River volcanics and the overlying greywackes of the Clayhole Creek beds, a contact that marks the cessation of volcanic activity. The local stratigraphy, from the base, comprises:
i). Surveyor rhyolite, which is typically a massive, glassy, aphanitic rhyolite, possibly representing a rhyolite dome;
ii). pyritic biotite-spotted quartz-sericite schist, representing altered lapilli tuff and coarse fragmental volcanics;
iii). Massive sulphide, which has a diffuse footwall with semi-massive and stringer sulphides in strongly silicified brecciated footwall volcanics, and a sharp hangingwall. They comprise coarsely recrystallised euhedral sphalerite with up to 15% insterstitial galena, 'buckshot' pyrite and 1 to 5% chalcopyrite, minor rare interstitial pyrrhotite, arsenopyrite and tetrahedrite. Gold is associated with copper and both are highest in grade in the core of the deposit. Massive magnetite is absent;
iv). Rhyolite fragmental, composed of sub-rounded to angular, tightly packed rhyolite fragments in a sericitic matrix with accassional disseminated pyrite and suphide clasts;
v). orbicular textured dacite, which is a massive lava flow characterised by red hematite altered ovate patches, often containing elongate dark fragments or quartz-carbonate filled vesicules;
vi). Upper metagreywacke.
Resources are as follows:
Balcooma - 3.5 Mt @ 3.0% Cu, with signigicant Zn and Pb. (Huston and Taylor, 1990)
Surveyor - 0.483 Mt @ 19.9% Zn, 8.8% Pb, 0.84% Cu,148 g/t Ag, 1.09 g/t Au. (Huston and Taylor, 1990)
Dry River South - 1.3 Mt @ 9.9% Zn, 3.6% Pb, 1.0% Cu. (Huston and Taylor, 1990)
Total Resource, Balcooma, Surveyor and Dry River South, 2003:
Polymetallic Ore - 3.877 Mt @ 1.10% Cu, 3.90% Pb, 8.94% Zn, 81 g/t Ag, 0.74 g/t Au. (Kagara Zinc web site, 2003)
Copper Ore - 2.342 Mt @ 3.44% Cu, 0.14% Pb, 0.34% Zn, 18 g/t Ag, 0.44 g/t Au. (Kagara Zinc web site, 2003)
Remaining JORC compliant reserves and resources (reserves additional to resources) at Balcooma in 2012 (Kagara Mining, 2012) were:
Proved copper reserves - 0.064 Mt @ 2.5% Cu, 13 g/t Ag;
Probable copper reserves - 0.130 Mt @ 1.6% Cu, 8 g/t Ag;
Measured copper resources - 0.235 Mt @ 2.9% Cu, 13 g/t Ag;
Indicated copper resources - 0.124 Mt @ 1.3% Cu, 5 g/t Ag;
Inferred copper resources - 0.053 Mt @ 0.7% Cu, 4 g/t Ag;
Probable polymetallic sulphide ore reserves- 0.027 Mt @ 9.2% Zn, 5.3% Pb, 0.6% Cu, 0.0 g/t Au, 35 g/t Ag;
Measured polymetallic sulphide ore resources - 0.389 Mt @ 5.7% Zn, 1.9% Pb, 1.1% Cu, 0.0 g/t Au, 26 g/t Ag;
Indicated polymetallic sulphide ore resources - 0.568 Mt @ 5.6% Zn, 2.2% Pb, 1.2% Cu, 0.3 g/t Au, 33 g/t Ag;
Inferred polymetallic sulphide ore resources - 0.575 Mt @ 3.1% Zn, 1.2% Pb, 1.5% Cu, 0.3 g/t Au, 24 g/t Ag;
TOTAL tonnage of ore - 2.165 Mt.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 2003.
Record last updated: 24/6/2013
This description is a summary from published sources, the chief of which are listed below.
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References to this deposit in the PGC Literature Collection:
Huston D L, Taylor T W 1990 - Dry River Copper and Lead-Zinc-Copper deposits: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1519-1526|
Huston D L, Taylor T, Fabray J, Patterson D J 1992 - A comparison of the geology and mineralization of the Balcooma and Dry River South volcanic-hosted massive sulfide deposits, northern Queensland: in Econ. Geol. v87 pp 785-811|
Large R R 1992 - Australian volcanic-hosted massive sulfide deposits: features, styles, and genetic models: in Econ. Geol. v87 pp 471-510|
Rea P S, Close R J 1998 - Surveyor 1 copper-lead-zinc-silver-gold-deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne Mono 22 pp 737-742|
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