Significant Copper-Gold Discovery at Munarra Gully
Perth, Aug 30, 2018 AEST (ABN Newswire) - Rumble Resources Ltd (
ASX:RTR) ("Rumble" or "the Company") is pleased to announce that RC drilling assays have been received from the recent Munarra Gully Cu-Au projects maiden drill program which consisted of seven (7) RC holes for 1149m. The Munarra Gully project is located some 50km NNE of the town of Cue within the Murchison Goldfields.
Very significant copper-gold RC drill intercepts discovered in fine to medium grain orthopyroxenitic rocks, potentially represents a style of magmatic sulphide mineralisation that is known to host large copper systems in Brazil and South Africa.
Lag and grab sampling by Rumble has outlined over 8km of strike potential coinciding with a partly buried strong magnetic anomaly which has been inferred as the same host - orthopyroxenite.
Munarra Gully - M51-0122 - White Rose Prospect - Cu-Au Discovery
Significant disseminated sulphide mineralisation in mafic intrusive rocks at the White Rose Prospect has returned:
- 22m @ 1% Cu from 29m coincident with 19m @ 2.19 g/t Au from 33m (WRRC001).
o Co-incident copper - gold mineralisation within orthopyroxenites includes 10m @ 3.41 g/t Au from 40m (maximum Au value 11.56 g/t) in WRRC001.
- All four RC drill-holes (two lines, 160m apart) completed at the White Rose Prospect returned strong copper-gold sulphide mineralisation in both oxide and primary zones. Other intercepts include:
o Co-incident copper - gold mineralisation - 10m @ 0.74% Cu from 75m with 11m @ 0.73 g/t Au from 75m (WRRC002).
o Co-incident copper - gold mineralisation - 26m @ 0.79% Cu from surface and 7m @ 0.64% Cu from 28m with 5m @ 1.17 g/t Au from 13m, 5m @ 0.71 g/t Au from 20m and 9m @ 1.64 g/t Au from 27m (WRRC003).
Potential Mafic Hosted Magmatic Sulphide System
- Copper and gold sulphide mineralisation associated with fine to medium grain undifferentiated orthopyroxenite/norite intrusive (mafic/ultramafic) rocks.
- Copper and gold are associated with chalcopyrite and bornite. The mineralisation has very high Cu:Ni ratios with strong silver anomalism (to 11.4 g/t Ag). Platinum group elements assay results are pending.
- The style of mineralisation has similar characteristics to known large copper rich mafic intrusive (ortho-pyroxenite) deposits in Brazil (Caraiba mining district - 96Mt @1.82% Cu reserve and historic production) and South Africa (Okiep mining district - Koperberg - 94Mt @ 1.75% Cu historic production). Gold, silver and PGM's are associated with these copper deposits (further detail page 5).
Lag Sampling highlights Mafic Hosted Cu-Au Sulphide Potential
- Lag (soil) sampling by Rumble has highlighted strong copper anomalism over 3.5km strike 4km to the southwest of the White Rose Prospect. Copper in lag anomalism (>400 ppm Cu) is supported by strongly anomalous Cu - Au grab sampling (Cu to 0.28% and Au to 2.11 g/t - no previous exploration or workings).
Rumble's Technical Director, Mr Brett Keillor, said "to have a significant copper-gold discovery with Rumble's maiden RC drilling programme at Munarra Gully is exceptional.
Discovering the copper-gold association with disseminated sulphides highlights the potential for economic copper-gold bearing mafic/ultramafic intrusive related mineralised systems. The mineralisation style bears close resemblance to known atypical magmatic sulphide systems worldwide where large world class copper (gold) deposits have been historically mined - the Caraiba Cu province in Brazil and the Okiep Cu province in South Africa are examples.
Within the Munarra Gully Project, Rumble has only tested a small section of a potential Cu - Au bearing intrusive system. Limited soil geochemistry and aero-magnetic interpretation has identified up to 8km of strike potential. Lag (soil) sampling over areas of less cover has highlighted 3.5km of significant copper anomalism.
The Munarra Gully project has all year round access and is close to major infrastructure and represents a potential discovery and Rumble will fast track systematic exploration to delineate first order copper-gold drill targets."
White Rose Cu-Au Prospect - New Cu-Au Discovery
Four (4) drill-holes (WRRC-001 to WRRC-004) were designed to test the primary zone below two small open cuts at the main White Rose Prospect. Two traverses, 160m apart were completed. Widespread copper and gold mineralisation in oxidised ultramafic/mafic had been exposed in the open cuts by the current owner. The open cuts (active operation) have a maximum depth of nearly 20m. Historic RAB drilling focused on gold and was confined to shallow oxide (vertical depth of 32m).
All drill-holes (four completed on the White Rose Prospect) intercepted widespread significant copper- gold mineralisation. See Images 2 and 3 in link below for sections.
- Copper and gold are associated with disseminated sulphide (chalcopyrite and bornite) mineralisation hosted in orthopyroxenite (norite) intrusive. RC drilling intercepts include:
o * WRRC001 - 22m @ 1% Cu from 29m coincident with 19m @ 2.19 g/t Au from 33m. Maximum Cu was 2.66% (40-41m). Maximum Au was 11.56 g/t (49-50m).
o * WRRC002 - 10m @ 0.74% Cu from 75m coincident with 11m @ 0.73 g/t Au from 75m.
o * WRRC003 - 26m @ 0.79% Cu from surface and 7m @ 0.64% Cu from 28m. In addition, 5m @ 1.17 g/t Au from 13m, 5m @ 0.71 g/t Au from 20m and 9m @ 1.64 g/t Au from 27m.
o * WRRC004 - 23m @ 0.54% Cu from 45m and 6m @ 0.66% Cu from 70m.
* 0.3% Cu and 0.3 g/t Au lower cut-off and true intercept width unknown
Approximately 160m to the west of the White Rose Prospect a single RC hole (WRRC007) tested the inferred strike of the copper-gold mineralisation. The hole intercepted a late dolerite dyke which has intruded into the prospective zone thereby displacing the inferred mineralisation (see image 1 in link below).
The disseminate sulphide mineralisation at White Rose is hosted in generally fine grain undifferentiated orthopyroxenite/norite to dolerite rock types. The rocks are magnetite bearing. Ag is strongly elevated (to 11.4 g/t Ag). PGE (platinum group elements) assay results are pending. The higher order copper-gold mineralisation lies within the mafic rocks immediately adjacent to the contact with ultramafic (>10% Mg) rocks.
The deposition style is considered very significant as it potentially represents copper bearing mafic/ultramafic intrusive related mineralisation. Examples include the Caraiba Cu mining district in Brazil (production and reserve - 96Mt @ 1.82% Cu) and the Okiep (Koperberg) Cu mining district in South Africa (historic production - 94Mt @ 1.75% Cu) - see overview section below.
Regional Geochemistry - E51/1677 (see image 4 in link below)
Rumble has conducted limited (400m by 100m spacing) lag geochemistry along the inferred mafic/ultramafic lithological horizon with additional grab sampling within E51/1677. The area is located 4km southwest of the White Rose Prospect. Lag sampling (107 samples taken) returned significant copper, nickel and gold anomalism. Copper returned up to 721 ppm in lag, nickel to 1800 ppm and Au to 72 ppb.
Copper anomalism over 3.5km in strike coincided with inferred mafic/ultramafic (orthopyroxenites) from aero- magnetics. Grab sampling along the copper in lag anomalism (only 3 samples collected) returned up to 2.11 g/t Au and 0.28% Cu. There were no previous exploration or historic workings associated with the grab sampling.
Large First Order Conductor (see image 1 in link below)
Two (2) holes were completed. The target is a large conductive plate (470m by 260m) that lies 600m west of the White Rose prospect. The first hole (WRRC-005 - 200m depth) missed the target due to the presence of a late dolerite dyke. The hole lifted from 70deg to 45deg and the azimuth moved 20deg.
The second hole (WRRC-006 - 289m depth) was completed by a larger capacity rig and was able to stay within tolerance with respect to intercepting the modelled conductor. Due to a blockage, the down-hole TEM survey (completed 25th August) was tested to 250m (down-hole depth). Results pending.
Overview of Mafic Intrusive Hosted Copper (Au, PGM) Sulphide Deposits (see References 1, 2, 3, 4 below)
In the Caraiba Complex, Bahia Province, Brazil, numerous mafic/ultramafic irregular shaped intrusions hosted chalcopyrite-bornite mineralisation (predominantly in orthopyroxenite). The total reserve for the complex (including historical production) is estimated at 96 Mt @ 1.82% Cu. The deposits are atypical of magmatic deposits in that magnetite may be up to 50%. The copper mineralisation is typically 70% chalcopyrite: 30% bornite. In addition, very high Cu:Ni ratios are the norm with associated Au, Ag and PGM's. Gold is reported to 22 g/t. The copper bearing intrusives are hosted in amphibolite/granulite rocks (ultra-high temperature metamorphics).
A similar style of copper mineralisation has been mined in the Okiep mining province in South Africa (Koperberg suite). Historically some 94 Mt @ 1.75% Cu was mined from predominantly orthopyroxenites associated with numerous irregular shaped mafic to ultramafic bodies with characteristic high Cu:Ni ratios and very strongly anomalous Au, Ag and PGM's.
Next Steps
Fast tracking exploration on the significant new Cu-Au discovery will involve:
- PGM assays - results are pending.
- DHEM - awaiting modelling and interpretation results.
Further surface geochemistry, geophysics and drilling will be conducted based on methodologies determined suitable by the above criteria.
References
1. Maier, Wolfgang & Barnes, Sarah-Jane. (1999). The origin of Cu sulfide deposits in the Curaca Valley, Bahia, Brazil: Evidence from Cu, Ni, Se, and platinum-group element concentrations. Economic Geology. 94. 165-183. 10.2113/gsecongeo.94.2.165.
2. Cawthorn R G, Meyer F M 1993 - Petrochemistry of the Okiep Copper district basic intrusive bodies, Northwestern Cape Province, South Africa: in Econ. Geol. v88 pp 590-605
3. Lombaard A F, Okiep Copper Company Limited 1986 - The copper deposits of the Okiep district, Namaqualand: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v2 pp 1421-1445
4. Maier W D 2000 - Platinum-group elements in Cu-sulphide ores at Carolusberg and East Okiep, Namaqualand, South Africa: in Mineralium Deposita v35 pp 422-429
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About Rumble Resources Ltd
Rumble Resources Limited (ASX:RTR) (FRA:20Z) is an Australian based exploration company, officially admitted to the ASX on the 1st July 2011. Rumble was established with the aim of adding significant value to its current gold and base metal assets and will continue to look at mineral acquisition opportunities both in Australia and abroad.
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