The Broken Hill orebody is the largest silver-lead-zinc deposit of its kind in the world. It is located in the southeastern part of the Curnamona Province in Proterozoic rocks around 1,700 million years old.
GCR has 100% of EL6518 located to the south-east of thew township of Broken Hill (see figure below). Through an extensive geological and geophysical database along with ground exploration three styles of minealisation are thought to be prospective in the tenement:
- Broken Hill-style mineralisation;
- High grade nickel-copper-platinum-palladium mineralisation; and
- Shear-hosted and iron oxide copper-gold mineralisation.
Vale (CVRD-Inco) – GCR Joint Venture
GCR’s joint venture in the southern half of the Broken Hill tenement was designed to primarily test the PGE rich Ni Cu sulphides associated with the Neoproterozoic ultramafic and mafic dykes and differentiated bodies intruded into the high grade metamorphic rocks of the Paleo- and Mesoproterozoic Willyama Supergroup. Other potential exploration targets include iron oxide copper gold (IOCG) deposits.
Based on previous drilling results the most significant Ni Cu-PGE prospects appears to be associated with ultramafic rocks at the Mt Darling Ck prospect and also within the Mulga Springs prospect. Previous diamond drilling and rock chip sampling at Mulga Springs has returned strongly mineralised PGE, Ni, Cu and anomalous Au values (unusually high gold values). This mineralisation is situated along the basal contact of an olivine rich cumulate ultramafic (UM) which has a width of up to 100m and is elongate and discontinuous along strike. The UM unit associated with the known mineralisation is thought to extend in a south easterly direction into the joint venture area and a review of the magnetic data indicates that close spaced magnetic data may be of use tracking the UM units under cover.
As part of the broader exploration review process three areas were identified where moving loop EM surveying was deemed appropriate to test potential feeder zones around known ultramafic bodies. These areas include Mt Darling Ck, coincident magnetic and gravity anomalies associated with malachite (green mineral) staining at Crows Nest and areas to the south of the Little Broken Hill Gabbro complex where there were gaps in the historical EM (electoral magnetic) data.
Data from the moving loop EM and reprocessing of the historical EM data failed to identify any conductive body that could be associated with massive sulphides. However initial field investigations have identified a number of mineralised locations, eg the Crows Nest prospect where malachite stained mafic rocks returned elevated values of copper and gold and a small magnetic feature with outcropping metagabbro which also returned elevated copper and gold values.
Further soil geochemistry in areas of residual soil and RAB/Aircore drilling in covered areas is required to test a number of magnetic targets adjacent or marginal to known ultramafic bodies. The detailed aeromagnetic data has helped to define the position of several geophysical anomalies which previous drilling identified as mafic lithologies below shallow transported material. Given their proximity to the Mulga Springs type location these anomalies are worthy of RAB drill testing.
Exploration by our Joint Venture partners over the past two years confirm the areas prospectivity for all three styles of mineralisation.
Drilling of ultramafic bodies by Vale at Little Broken Hill Gabbro returned anomalous copper and nickel values across several holes. In addition the drilling confirmed the extension of the ultramafics under cover opening up the potential for hidden mineralisation elsewhere in the tenement.
History
Historically, work has focused on exploration for the Broken Hill-style Pb-Zn-Ag mineralisation, however a number of campaigns in the 1970’s and 1980’s recognised the association of small PGE-Ni-Cu gossans associated with intrusive mafic-ultramafic complexes which are probably about 600 to 700 million years old, much younger than the Broken Hill host rocks.
Sampling of these gossans returned spectacular grades of PGE’s and gold, commonly over 15 g/t combined. In the 1970’s CRA drilled a diamond hole into the Mulga Springs prospect and recorded a two to three metre intersection of banded pyrrhotite磁黄铁矿-pendlandite镍黄铁矿-chalcopyrite黄铜矿associated with cumulate textured olivine rich mafic rocks.
Whilst the tenor of this hole was assessed, no systematic analyses for PGE’s were undertaken. GCR undertook to drill a hole close by in 2001 and returned an intersection of 2m at 10.9 g/t platinum, 23.6 g/t palladium, 0.94 g/t gold, 6.12% copper and 4.45% nickel in massive sulphide.
Geological mapping by the NSW geological survey had outlined a discontinuous, locally highly sheared zone of mafic rocks extending from Mulga Springs, almost 9km to the northwest to the Moorkaie prospect. GCR undertook prospecting over this zone and discovered a number of previously unmapped mafic intrusions and gossans which returned highly anomalous PGE’s. The Back Ridge gossan returned 40g/t Pt+Pd for example.
At about this time GCR undertook to consolidate tenure in the district and secured at large licence to the south which hosted the Little Darling Creek PGE zone also assessed during the 1980’s. From 2003 to 2005 a joint venture with Sipa Resources led to accumulation of more ground, in particular, the Red Hill and Little Broken Hill Gabbro prospects, both hosting PGE-bearing mafic-ultramafic complexes. Sipa undertook ground EM surveys over Mulga Springs and the Moorkaie Prospects and drilled holes at Mulga Springs, Mulga West and Round Hill. Drilling proved unsuccessful however a distinct EM anomaly was detected on the down plunge extension of surface mineralisation at Moorkaie.
Vale (CVRD-Inco) – GCR Joint Venture
In 2006 a joint venture with Inco/CVRD, now Vale,was formalised to work on the southern portion of the tenement. The joint venture was designed to primarily test the PGE rich Ni Cu sulphides associated with the Neoproterozoic ultramafic and mafic dykes and differentiated bodies intruded into the high grade metamorphic rocks of the Paleo- and Mesoproterozoic Willyama Supergroup. Other potential exploration targets include iron oxide copper gold (IOCG) deposits.
Based on previous drilling results the most significant Ni Cu-PGE prospects appears to be associated with ultramafic rocks at the Mt Darling Ck prospect and also within the Mulga Springs prospect. Previous diamond drilling and rock chip sampling at Mulga Springs has returned strongly mineralised PGE, Ni, Cu and anomalous Au values (unusually high gold values). This mineralisation is situated along the basal contact of an olivine rich cumulate ultramafic (UM) which has a width of up to 100m and is elongate and discontinuous along strike. The UM unit associated with the known mineralisation is thought to extend in a south easterly direction into the joint venture area and a review of the magnetic data indicates that close spaced magnetic data may be of use tracking the UM units under cover.
As part of the broader exploration review process three areas were identified where moving loop EM surveying was deemed appropriate to test potential feeder zones around known ultramafic bodies. These areas include Mt Darling Ck, coincident magnetic and gravity anomalies associated with malachite (green mineral) staining at Crows Nest and areas to the south of the Little Broken Hill Gabbro complex where there were gaps in the historical EM (electoral magnetic) data.
Data from the moving loop EM and reprocessing of the historical EM data failed to identify any conductive body that could be associated with massive sulphides. However initial field investigations have identified a number of mineralised locations, eg the Crows Nest prospect where malachite stained mafic rocks returned elevated values of copper and gold and a small magnetic feature with outcropping metagabbro which also returned elevated copper and gold values.
Further soil geochemistry in areas of residual soil and RAB/Aircore drilling in covered areas is required to test a number of magnetic targets adjacent or marginal to known ultramafic bodies. The detailed aeromagnetic data has helped to define the position of several geophysical anomalies which previous drilling identified as mafic lithologies below shallow transported material. Given their proximity to the Mulga Springs type location these anomalies are worthy of RAB drill testing.
Exploration by our Joint Venture partners over the past two years confirm the areas prospectivity for all three styles of mineralisation.
Drilling of ultramafic bodies by Vale at Little Broken Hill Gabbro returned anomalous copper and nickel values across several holes. In addition the drilling confirmed the extension of the ultramafics under cover opening up the potential for hidden mineralisation elsewhere in the tenement.
History
Historically, work has focused on exploration for the Broken Hill-style Pb-Zn-Ag mineralisation, however a number of campaigns in the 1970’s and 1980’s recognised the association of small PGE-Ni-Cu gossans associated with intrusive mafic-ultramafic complexes which are probably about 600 to 700 million years old, much younger than the Broken Hill host rocks.
Sampling of these gossans returned spectacular grades of PGE’s and gold, commonly over 15 g/t combined. In the 1970’s CRA drilled a diamond hole into the Mulga Springs prospect and recorded a two to three metre intersection of banded pyrrhotite磁黄铁矿-pendlandite镍黄铁矿-chalcopyrite黄铜矿associated with cumulate textured olivine rich mafic rocks.
Whilst the tenor of this hole was assessed, no systematic analyses for PGE’s were undertaken. GCR undertook to drill a hole close by in 2001 and returned an intersection of 2m at 10.9 g/t platinum, 23.6 g/t palladium, 0.94 g/t gold, 6.12% copper and 4.45% nickel in massive sulphide.
Geological mapping by the NSW geological survey had outlined a discontinuous, locally highly sheared zone of mafic rocks extending from Mulga Springs, almost 9km to the northwest to the Moorkaie prospect. GCR undertook prospecting over this zone and discovered a number of previously unmapped mafic intrusions and gossans which returned highly anomalous PGE’s. The Back Ridge gossan returned 40g/t Pt+Pd for example.
At about this time GCR undertook to consolidate tenure in the district and secured at large licence to the south which hosted the Little Darling Creek PGE zone also assessed during the 1980’s. From 2003 to 2005 a joint venture with Sipa Resources led to accumulation of more ground, in particular, the Red Hill and Little Broken Hill Gabbro prospects, both hosting PGE-bearing mafic-ultramafic complexes. Sipa undertook ground EM surveys over Mulga Springs and the Moorkaie Prospects and drilled holes at Mulga Springs, Mulga West and Round Hill. Drilling proved unsuccessful however a distinct EM anomaly was detected on the down plunge extension of surface mineralisation at Moorkaie.
Geology
EL6518 is situated near the eastern margin of the Broken Hill Block which is the exposed SE portion of the Curnamona Craton. It contains high grade metasediments and intrusives which are collectively referred to as the Willyama Supergroup. Bedrock exposures are typically quite fresh, with few areas of deep saprolite. The main stratiform mineral deposits are intimately related to stratigraphic units with the Broken Hill Group hosting the Broken Hill lode (279Mt @ 2-5%Pb, 5- 20% Zn, 20-300g/t Ag).
The region under went deformation (D1+D2) and high grade granulite facies metamorphism around 1600Ma (million years) ago which remobilised some of the mineral deposits and produced pegmatite intrusions. Retrograde shearing, metamorphism and upright open folding associated with later stage deformation (D3) occurred at around 1570Ma and also led to emplacement of some vein type deposits. Further retrograde shearing occurred around 520 Ma and was synchronous with the Delamerian Orogeny
The Willyama Supergroup represents a predominantly terrigenous（陆源的）, clastic（可分解的，碎屑状的） depositional 沉积的，沉淀的sequence顺序 laid down in an intracratonic古陆内的 rift 裂痕during the interval 1720Ma to 1640Ma. Its stratigraphic succession has been questioned recently by some workers who interpret early thrusts and multiple high-grade metamorphic events. However, latest geochronology, employing high precision methods and carefully constrained sample selection, does not offer any support to these complex models. Rather, it appears to be fully consistent with the proposed stratigraphy.
The entire exposed Broken Hill Block has been mapped in detail at 1:25,000 by workers of the New South Wales Department of Mineral Resources (NSWDMR). Together with other data of relevance to exploration, this mapping has been released as GIS coverages through the Broken Hill Exploration Initiative in collaboration with Geoscience Australia (formerly AGSO). The exposed Proterozoic rocks within EL6518 have been mapped by NSWDMR as Thorndale Gneiss, Cues Formation, Himalaya Formation and Purnamoota SubGroup. All but the last are interpreted to be part of the Thackaringa Group, within the lower stratigraphy of the Willyama Supergroup. The Purnamoota Subgroup is interpreted to be a distal (long way away)equivalent of the Broken Hill Group A suite of variably deformed mafic and ultramafic intrusions occurs within the Willyama Supergroup. P group is similar to W group but just long way away
These dykes are relatively low metamorphic grade and definitely post-date granitic花岗岩的 intrusives and related pegmatites. Although previously regarded as Cambrian in age the mafic ultramafic intrusives were recently dated at 827 Ma approximately coeval with the Gardner dyke swarm (geo event) and Rhodinia (age)breakup(geo event). The dated sample was derived from the “Little Broken Hill Gabbro.
Ultramafic Intrusives
There are 4 main mafic/ultramafic intrusions in the tenement area of which 3 are associated with PGE rich gossans after Ni-Cu sulphides. These are in the vicinity of Mt Darling Creek, in the NW part of the tenement (and at Mulga Springs, some 3km to the N) and at Red Hill, with the Little Broken Hill Gabbro representing the largest body of rock but with no known mineralised association. The larger ultramafic bodies are now mostly serpentinites or chlorite-amphibole rocks after peridotites and pyroxenites, respectively. Smaller and thinner dykes tend to be doleritic in texture, particularly those forming NW-SE and SSW-NNE dyke swarms. Numerous, variably oriented shear zones cut the metamorphics. These also post-date the mafic-ultramafic dykes, at least in terms of their latest movement. They are marked in the field by intense schistose 片岩的deformation and retrograde mineral assemblages聚集. The shears are interpreted to be the result of the superimposed Cambro-Ordovician Delamerian Orogeny (~520-480Ma). This orogeny is believed to be related to accretion of various
Phanerozoic 显生宙sequences onto the eastern margin of the Curnamona Province.
Some of the ultramafics are strongly magnetic and contain coarse magnetite. In others, the opaque is magnetite-coated chromite. While there is excellent preservation of cumulate textures in some areas (particularly within central parts of pod-like masses) most are strongly schistose or even composed of crenulated phyllite near contacts. Foliations are generally parallel to dyke margins. Talc云母 and talc dolomite白云石 alteration occurs locally. Pits are commonly developed on some coarse grained magnesite pods and rare fibrous white asbestos veins.
Joint Ventures
In October 2010 GCR farmed out Exploration Licence 7390 near Broken Hill to Silver City Minerals (SCI). SCI identified a potential drill target within a steeply dipping ironstone and siliceous gossan horizon at Yellowstone, hosted within the Yellowstone Shear Zone. Previous work had located anomalous copper and gold rock chip samples at surface (up to 16 g/t gold) and shallow historic drilling hosted similarly anomalous samples most of which occurred in the oxide zone (for example 8 metres of 0.59% copper and 1 metre of 8.61 g/t gold).
As a prelude to drilling, SCI conducted a larger IP survey and soil geochemical sampling in order to identify other potential sulphide-bearing zones within the Shear Zone. A number of chargeability anomalies were identified and, in particular, a one kilometre long anomaly was identified that included mineralisation intersected in previous drilling and the outcropping gossan.
Drilling encountered pyrite (iron sulphide) mineralisation in holes 09, 10, 12 and 13. Significant results are as follows:
- 4 metres at 1.5 g/t gold and 0.2% copper from 68 metres in hole YE009.
- 4 metres at 54.2 g/t silver and 0.15% copper from 73 metres in hole YE010.
Yellowstone IP survey. Chargeability response modelled at approximately 100 metres below surface.
Diagram shows the location of both historic and recent Silver City holes.
Endeavour Minerals has the right to explore Exploration Licence 7390 for platinum group elements and nickel only. Endeavour conducted surface sampling of soil and rock chips at the Little Broken Hill Gabbro, Round Hill, Little Darling Creek and at Back Ridge & Southern Slope, north of Mulga Springs.
The program in-filled and extended previous sampling programs seeking anomalous areas that might contain extensions of mineralised ultra-mafic rocks under cover and to assist in the design of a subsequent drilling program.
Updated February 2013