Mabilo copper-gold-iron skarn deposit, Philippines

Mabilo is a significant Cu-Au-Fe discovery in the Paracale district of southern Luzon Island.  The currently defined (indicated) resource is 8.86 Mt @ 1.9% Cu, 2 g/t Au, 9.8 g/t Ag and 45.6% Fe.

Mabilo is a significant Cu-Au-Fe discovery in the Paracale district of southern Luzon Island. The currently defined (indicated) resource is 8.86 Mt @ 1.9% Cu, 2 g/t Au, 9.8 g/t Ag and 45.6% Fe.

Robert McClean sited the first drill-hole at Mabilo as a consultant to ASX-listed Sierra Mining Ltd in 2012, prior to its takeover by RTG Mining. Initial targeting was based on magnetic data acquisition and modelling completed by previous project managers in 2007. The first magnetic target drilled by Sierra intersected 94 m at 2.2% Cu and 1.6 g/t Au and 36.6% Fe under 20 m of Labo volcanic cover, 500 m south of the Venida Pit. Subsequent drilling of nearby magnetic targets intersected only minor oxidised mineralisation and minor altered skarn and dolerite.

At this point SGC was asked to review the magnetic data and modelling over Mabilo. The 2012 review highlighted a number of data QC issues including;

  • Unsuitable survey line direction given the orientation of the local inducing field
  • Incorrect orientation of the magnetic sensor with respect to the inducing field
  • Incorrect locating (interpolation) of the data points locations on several survey lines
  • Interference from surficial magnetic sources due to low ground clearance
  • Inadequate line spacing to properly delineate the magnetic targets.

These issues seriously undermined the value of the data and subsequent modelling and drill targeting. Given the significance of the intersections and the importance of the magnetic data with respect to targeting, SGC recommended that the survey be repeated.

SGC arranged the purchase of new equipment and on-site training of in-house operators to carry out a new survey; this provided the client with greater flexibility for acquiring data over the Mabilo and other projects. On-site training was completed by SGC Principal Geophysicist Greg Maude in March 2013 and the crew continued data acquisition over the following months, supervised and supported remotely by the SGC team.

Due to the deposit being essentially ‘blind’ (covered by 20 to 30 m of volcanic cover), 2D and 3D modelling of the magnetic data was the primary targeting tool, and successfully delineated the highly magnetic skarn mineralisation.

DeGrussa copper-gold mine, Bryah Basin, WA

Exploration on Sandfire Resources’ Doolgunna Project in Western Australia’s Bryah Basin started in 2004 and was focussed on the gold potential of the area. Soil geochemistry and shallow RAB drilling completed between 2004 and 2008 began to refine a gold anomaly which was also highly anomalous for most metals, particularly copper. The shallow drilling delineated a sequence of saprolitic clay and sheared volcaniclastic sediments of the Paleoproterozoic Narracoota Volcanic Formation. A combined SAM-ground magnetic survey over the gold anomaly failed to identify much of interest with results dominated by responses of the conductive and weakly magnetic transported cover.

Exploration on Sandfire Resources’ Doolgunna Project in Western Australia’s Bryah Basin started in 2004 and was focussed on the gold potential of the area. Soil geochemistry and shallow RAB drilling completed between 2004 and 2008 began to refine a gold anomaly which was also highly anomalous for most metals, particularly copper. The shallow drilling delineated a sequence of saprolitic clay and sheared volcaniclastic sediments of the Paleoproterozoic Narracoota Volcanic Formation. A combined SAM-ground magnetic survey over the gold anomaly failed to identify much of interest with results dominated by responses of the conductive and weakly magnetic transported cover.

An RC program commenced in April 2009 to test the broad zone of gold anomalism, and in May 2009, discovery drillhole DGRC083 intersected significant high-grade copper and gold mineralisation (including 19 m @ 4.2 g/t Au from 4 m including 12 m @ 6.2 g/t from 40 m).

Senior Consulting Geophysicist Bill Peters then became involved with the project and commenced geophysical exploration with downhole EM surveying in order to gain an understanding of the geometry and size of the mineralisation. Fixed and moving loop ground surveys were also carried out to extend EM coverage. The intersected DeGrussa massive sulfide mineralisation was detected and named Conductor 2; however a larger surface EM anomaly was also identified to the north and called Conductor 1. Drilling of Conductor 1 confirmed a new massive sulfide body north and below DeGrussa (Conductor 2). The first diamond drilling intersected spectacular high grade Cu-Au results including 8 m at 27.3% Cu, 1.9 g/t Au and 34.9 g/t Ag in DGDD-001. A further conductor, Conductor 4, was identified below Conductor 1 from downhole EM surveying. Subsequent drilling confirmed Conductor 4 as a third significant massive sulfide deposit in November 2009.

Follow-up regional airborne EM (VTEM) surveying detected the conductive massive sulfides, and generated additional regional targets, although the results showed DeGrussa was not an easy airborne target.

Subsequent geophysical work directed by SGC included a detailed aeromagnetic survey, an IP survey, a SAMSON EM survey, a gravity survey and physical property testing.

In June 2011, the DeGrussa Project had a total mineral resource of 14.33 Mt grading 4.6% Cu and 1.6 g/t Au, for 652,000 tonnes contained copper and 742,000 oz contained gold. Mining of DeGrussa’s DSO material commenced in February 2012 with the open-pit completed in April 2013 seeing the transition to a wholly underground mining operation.

B2 epithermal gold discovery, Philippines

The B2 discovery is part of Medusa Mining’s Tambis Project in Eastern Mindanao, Philippines. Gold mineralisation is associated with an intermediate sulfidation epithermal system and was first reported from diamond drillhole TDH279 in April 2013. The intersection included 12.4 m at 7.69 g/t Au and 8 m at 3.16 g/t Au occurring in andesitic diatreme breccia rocks. The drillhole was located over of a priority surface induced polarisation (IP) target modelled at >100 m depth below post-mineralisation limestone and sedimentary cover, and drill tested as part of a sterilisation program.

The B2 discovery is part of Medusa Mining’s Tambis Project in Eastern Mindanao, Philippines. Gold mineralisation is associated with an intermediate sulfidation epithermal system and was first reported from diamond drillhole TDH279 in April 2013. The intersection included 12.4 m at 7.69 g/t Au and 8 m at 3.16 g/t Au occurring in andesitic diatreme breccia rocks. The drillhole was located over of a priority surface induced polarisation (IP) target modelled at >100 m depth below post-mineralisation limestone and sedimentary cover, and drill tested as part of a sterilisation program.

Medusa geologists had identified the area for its potential to host a continuation of the diatreme breccia hosted Bananghilig (B1) gold deposit beneath overlying basin cover sequence. The B1 deposit outcrops approximately 1.5 km to the northwest of B2 and has a total (indicated and inferred) resource of 24.52 Mt at 1.40 g/t Au for 1,136,000 oz Au.

Principal Geophysicist, Anne Tomlinson, worked closely with Medusa geologists in the planning and acquisition of 2D dipole-dipole IP and ground magnetic programs at the Tambis project, as well as a number of other projects in their extensive tenement holdings in the region over several years. The work included petrophysical drill core testing, site visits, on-going QC of the data, 2D and 3D modelling, integrated interpretation of IP, magnetic and geological data, and 3D visualisation resulting in target identification and drill testing recommendations.

The last drill program was completed in June 2014. Trial downhole geophysical surveying, including electromagnetic (EM) and magnetometric resistivity (MMR), has been planned to investigate the potential to delineate additional higher gold grade hydrothermal breccia zones within the general B2 discovery area and has yet to be completed.

Cosmos nickel-copper mine, Leinster, WA

Cosmos is a typical komatiite-associated, highly conductive and magnetic, massive pyrrhotite-pentlandite nickel-copper sulfide deposit. It is located approximately 40 km south of the Mt Keith nickel mine in the Norseman-Wiluna greenstone belt of the northern Yilgarn Craton, Western Australia. It was discovered in mid-1997 by a team including Jubilee Mines geologists Tony Rovira and Terry Grammer and Consulting Geophysicist Bruce Craven, using a combination of geological, geochemical and geophysical exploration techniques during routine evaluation of a prospective ultramafic belt.

Cosmos is a typical komatiite-associated, highly conductive and magnetic, massive pyrrhotite-pentlandite nickel-copper sulfide deposit. It is located approximately 40 km south of the Mt Keith nickel mine in the Norseman-Wiluna greenstone belt of the northern Yilgarn Craton, Western Australia. It was discovered in mid-1997 by a team including Jubilee Mines geologists Tony Rovira and Terry Grammer and Consulting Geophysicist Bruce Craven, using a combination of geological, geochemical and geophysical exploration techniques during routine evaluation of a prospective ultramafic belt.

The discovery hole, JCD-001, was the initial test of a short strike-length, late-time transient electromagnetic (TEM) anomaly in an area that had previously been partially drill tested by other companies including Jubilee. It intersected ~9 m of massive and disseminated pyrrhotite-pentlandite mineralisation, including 3 m grading 7.5% Ni, close to the target depth predicted by the TEM modelling.  The second diamond hole, JCD-002, drilled on line 6944540N, encountered over 22 m of massive nickeliferous sulfides, including an intersection of 18 m at 10.67% Ni.

The original moving loop TEM anomaly, recognised on two 150 m spaced lines, was defined in detail using a large, fixed transmitter loop survey. Modelling of the late-time fixed-loop data indicated that the source was a steeply east dipping conductor at about 50-75 m depth.

Ore-grade massive nickel sulfides were intersected in the predicted position in the first diamond hole drilled to test the conductor. The limited depth extent of the conductor suggested by the modelling was confirmed by subsequent drilling and downhole TEM surveys. Detailed ground and aeromagnetic data subsequently collected over the deposit defined the host ultramafic well, but did not clearly distinguish the magnetic massive sulfide zone.

The significance of the Cosmos TEM surveys was their ability to quickly and accurately focus drilling on the small but high-grade massive sulfide lens within the much larger mineralised halo.

Subsequent geophysical exploration, primarily ground and downhole EM, resulted in further massive nickel sulphide discoveries including the Cosmos Deeps, Alex Mairs and Prospero deposits.

Jubilee Mines NL commenced production at Cosmos in 2000.  Jubilee was subsequently purchased by Xstrata Nickel in February 2008.

Thunder Bay North PGE deposit, Midcontinent Rift, Canada

The Thunder Bay North (TBN) project is located in the Midcontinent Rift of northwest Ontario, Canada, and is an ultramafic-hosted orthomagmatic nickel-copper-platinum group element deposit. Glacially transported ultramafic boulders containing abundant disseminated sulfides were first located within the southern part of the TBN claim block in July 2001 b y Magma Metals. Assays averaged 3.8g/t Pt+Pd+Au, 0.2% Ni and 0.4% Cu. A further occurrence of boulders, which appeared to be largely in situ, was found on the eastern shore of Current Lake in 2006.

The Thunder Bay North (TBN) project is located in the Midcontinent Rift of northwest Ontario, Canada, and is an ultramafic-hosted orthomagmatic nickel-copper-platinum group element deposit.

Glacially transported ultramafic boulders containing abundant disseminated sulfides were first located within the southern part of the TBN claim block in July 2001 b y Magma Metals. Assays averaged 3.8g/t Pt+Pd+Au, 0.2% Ni and 0.4% Cu. A further occurrence of boulders, which appeared to be largely in situ, was found on the eastern shore of Current Lake in 2006.

Due to the magnetic nature of the ultramafic host rock, a detailed aeromagnetic survey of the project was planned by Senior Consulting Geophysicist Bill Peters for Magma Metals with the aim of delineating the potential bedrock source. The survey was flown in July 2006 and immediately mapped out a prominent linear magnetic feature beneath Current Lake and a bullseye magnetic feature southeast of the lake, which were interpreted as the source peridotite intrusion.

The first hole, TBND001, was drilled into the magnetic anomaly in December 2006 confirming the peridotite intrusive and intersecting the discovery mineralisation which returned 10.5m @ 2.8 g/t Pt+Pd+Au, 0.5% Cu and 0.3% Ni.

Between 2006 and 2011 airborne, surface and, in particular, downhole EM methods were all subsequently used under the direction of SGC at the deposit to assist with directly targeting conductive sulfide mineralisation, as well as induced polarisation (IP). Physical property testing, downhole property logging, surface magnetics, downhole magnetometric resistivity (MMR), VTEM, and ZTEM methods have all also been applied.

The host peridotite and sulfide mineralisation are now recognised as part of the ~6 km long Current Lake Intrusive Complex. Two additional complexes were also identified by further aeromagnetic surveying to the west.

The TBN project is now owned by Panoramic Resources and at 30th September 2015 had a resource containing 10.4 Mt at 1.13 g/t Pt and 1.07 g/t Pd for ~0.4 Moz Pt and ~0.4 Moz Pd. The project is currently in joint venture with Rio Tinto Exploration Canada who is operating the exploration program.

Emily Ann nickel mine, Lake Johnston, WA

Geophysical techniques played a significant role in the discovery of the Emily Ann massive nickel sulfide deposit and extensions to the Maggie Hays deposit (Maggie Hay North), which are associated with komatiitic olivine cumulate ultramafic rocks, in the Lake Johnston Archean greenstone belt located about 500 km east of Perth in Western Australia’s Yilgarn craton.

Geophysical techniques, particularly electromagnetics (EM) and magnetics, played a significant role in the discovery of the Emily Ann massive nickel sulfide deposit and extensions to the Maggie Hays deposit (Maggie Hay North), which are associated with komatiitic olivine cumulate ultramafic rocks, in the Lake Johnston Archean greenstone belt located about 500 km east of Perth in Western Australia’s Yilgarn craton.

The Maggie Hays deposit contained inferred and indicated resources of 11.9 Mt at 1.47% Ni, comprising a main disseminated and massive-sulfide zone and a northern massive sulfide-stringer zone. The Emily Ann deposit contained inferred and indicated resources of 2.17 Mt at 3.71% Ni and is predominantly massive sulfides.

SGC Consulting Geophysicist, Bill Peters, commenced geophysical work on the project for Forrestania Gold NL in 1992 and continued working on the project until 2002 at which time it was owned by LionOre Australia.

The Maggie Hays deposit comprises both disseminated and massive nickel sulfides concentrated at the base of an ultramafic unit 200-500 m below the surface. A limited moving-loop TEM survey in 1992 for Forrestania Gold located an anomaly immediately north of the main part of the deposit. In 1995, a fixed-loop TEM survey confirmed the earlier moving-loop anomaly as an excellent response, which when drilled, resulted in the discovery of the Maggie Hays North deposit 100 m below the surface.

A moving-loop TEM survey in 1996 resulted in the discovery of the blind, high-grade Emily Ann nickel sulfide deposit 3 km north of the Maggie Hays deposit, at a depth of 120 m.  Downhole TEM surveys aided delineation diamond drilling of the deposits with the location of extensions of mineralisation.

Other geophysical surveys carried out on the projects included IP, magnetics, MT, and AEM.

Production at Emily Ann began in late 2001 by LionOre and ceased in March 2007. LionOre was taken over by Norilsk Nickel in mid-2007. The Emily Ann and Maggie Hays deposits have been on care and maintenance since April 2013 and were purchased by Poseidon Nickel in mid-2014.

Grib diamond mine, Karelia, Russia

The Grib diamond mine, located in the Republic of Karelia in the Arkhangelsk Oblast of northwest Russia, is one of the largest diamond mines in the world.  The mine has estimated reserves of 98.5 million carats of diamonds and an annual production capacity of 3.62 million carats.

The Grib diamond mine, located in the Republic of Karelia in the Arkhangelsk Oblast of northwest Russia, is one of the largest diamond mines in the world.  The mine has estimated reserves of 98.5 million carats of diamonds and an annual production capacity of 3.62 million carats.

SGC consulted to Archangel Diamond Corporation between 1994 and 1998 processing and interpreting ground and airborne magnetic surveys. All geophysical data were collected by local Russian crews and contractors with the data being digitised, processed and interpreted by SGC as it became available.

In January 1996, data from a new heliborne magnetic survey was interpreted by Senior Consulting Geophysicist Bill Peters who selected 29 targets for follow-up.

In February 1996, drilling of one of these targets, V18, resulted in the discovery of a large kimberlite pipe which was later named Grib. The pipe is beneath 50-80 m of Quaternary cover with no indicator minerals as tracers. The deposit is now known to be comprised of two kimberlite pipes: Grib Pipe and North Pipe. The Grib Pipe is 57 Ha in size.

The mine is now owned and operated by Lukoil through its subsidiary Arkhangelskgeoldobycha (AGD).

Radio Hill nickel-copper mine, Western Pilbara, WA

The Radio Hill nickel-copper deposit is situated approximately 30 km south of Karratha in Western Australia. The orthomagmatic deposit is hosted within one of several mafic/ultramafic intrusions emplaced in the Archaean sequence of the western Pilbara Block.

The Radio Hill nickel-copper deposit is situated approximately 30 km south of Karratha in Western Australia. The orthomagmatic deposit is hosted within one of several mafic/ultramafic intrusions emplaced in the Archaean sequence of the western Pilbara Block.

It was originally located by Westfield Minerals in 1972 as an aeromagnetic anomaly with coincident weak Ni-Cu soil geochemistry in an area of no outcrop. Between that time and 1978 various geophysical surveys and drilling failed to locate significant mineralisation.

Between 1981 and 1986 geophysical surveys and drilling by Teck Explorations Limited and Samim Australia Pty Ltd, who engaged Senior Consulting Geophysicist Bill Peters, led to the discovery of a significant Ni-Cu sulfide deposit.

Geophysical surveying included airborne and ground magnetic surveys which mapped out the magnetic mafic/ultramafic intrusion. Surface EM surveys (SIROTEM) delineated two excellent conductors, Conductor A and Conductor B, in 1982. Drilling of the peaks of these anomalies intersected marginal sulphide mineralisation.

In 1984 an applied potential (mise-a-la-masse) survey also delineated the two separate conductive bodies, but with improved plunge and dip information. The discovery drillhole, RH207, was drilled into Conductor B in 1984 and intersected 18 m at 3.95% Ni+Cu at 160 m. The initial estimated resource was ~ 2.5 Mt @ 1.5% Ni and 1.4% Cu.

The Radio Hill mine was built in 1988 by AGIP. Subsequently Titan Resources Ltd and Fox Resources Ltd have operated the mine at different stages before going into care and maintenance in 2008.