• Field assessment of the ”Loaded Dog’ magnetic/geochemical (Cu-Pb-Zn) target confirms potential for a large porphyry-type deposit
• Cross-sections generated from drilling at Greendale Prospect indicate base metal mineralisation open along a fault strike and down dip
• Joint Venture with Richmond Mining Limited executed in March 2008 

Setting

The Mayfield North exploration area (EL 6691) abuts the Mayfield tenement (EL 6358) – see Figure 1. A number of polymetallic vein type or shear-zone hosted and VHMS type deposits were discovered within EL 6691 by previous explorers.

Figure 1: Tenements over shuttle radar terrain model

Location

The project area is located approximately 60km east of Canberra, immediately east of the Woodlawn Mine, a world-class VHMS Zn-Pb-Cu deposit with a reported 18Mt of historical production and current resource estimate of 10.1Mt @ 16.9% Zn equivalent.

Geology

The Early Silurian to Early Devonian granodioritic batholiths intrude the Ordovician turbidites. Bedrock geology is illustrated in Figure 2. More locally, smaller stocks also intrude the arenaceous sandstones, shales and siltstones of the Early Silurian to Middle Devonian Basin deposits. A major fault strikes N-SSW from Lake Bathurst town in the north, through Tarago and Mulloon in the south.

Figure 2: Bedrock geology

Bands of the Late Silurian porphyritic rhyolite/dacite volcanic unit, which hosts the Woodlawn deposit, are folded on N-S axes west of this fault. Other Silurian and Devonian felsic volcanic units are mapped more locally, in the extreme northeast of EL6691, near Windellama, and extending beyond the southern limits of the tenement, along a batholith margin.

Previous exploration

During the 1970’s, Asarco and other exploration companies discovered a large magnetic and geochemical anomaly termed ‘Loaded Dog’, which occurs in the central south of the Mayfield North licence. Exposures of sediments with intercalated sericitised (aplitic?) quartz porphyry and possible silicified tuff or carbonate were found.

Drilling at Greendale Prospect, which occurs in the northeast of EL 6691, near Budjong Prospect, was carried out in 1996/97 by Michelago Resources NL (and Denehurst Limited). This has indicated a potential for significant base metal mineralization, which was open at depth and along strike. A 10m-interval of the RC Hole GD-7 was reported to have intersected 7.23% Pb including 3m @ 13.87% Pb.

Exploration Activities Conducted by Monaro Mining

NSW Government generated airborne magnetic data was imaged and the historic stream sediment data was also contoured. The integration and interpretation of these data sets, together with other data gathered by previous explorers, has highlighted several regional targets for follow up. This includes the Loaded Dog anomaly, which appears to be a sub-outcropping discrete intrusive body and is considered to be prospective porphyry Cu-Au type target.

Recent fieldwork has confirmed the existence of the sericitised felsic, rhyodacitic rocks, with fine disseminated iron-oxides, which crop out sporadically within a 0.5km wide and 1.5km long N-S oriented zone. This zone appears to be open to the south, which is yet to be confirmed by further fieldwork. The preliminary air photo interpretation integrated with aerial magnetic image suggests that the rhyodacite suboutcrop zone extends by another ~2km in the SSE direction and ~1km to the WSW, underlying a prominent hill and a radial drainage pattern. It appears that the volcanics are flanked and probably overlain by steeply dipping shales and siltstones, which are often silicified and, in places, appear cherty.

Figure 3: Loaded Dog anomaly over airborne magnetic image

The shales and siltstones are locally interbedded with white, tuffaceous and clayey sequences. Gossanous, limonitic ironstone boulders were found in few places along the western boundary between the volcanics and shales. A granodioritic rocky outcrop was found at the southeastern end of the target area. Further to the southwest, this granodiorite is gradually altered to an increasingly softer rock, comprising quartz phenocrysts and accessory biotite in a very fine white clayey matrix. This zone appears to coincide with the faulted southern margin of the Loaded Dog anomaly.

The current interpretation is that the Loaded Dog target may represent a rhyodacitic dome, and is therefore highly prospective for a porphyry-related copper-gold. Further field mapping is to be carried out to better establish the extent and nature of the felsic volcanic zone. Magnetic susceptibility measurements of rock samples and ground geophysical surveying will assist in a more precise delineation of zones suitable for drilling. Profiles derived from the historic magnetic data suggest that the source of the Loaded Dog anomaly is the top of a stock or a flat body (sill or mineralization). Irregularities in the profile suggest that discrete units occur within this body.

Spectral measurements of rock samples (Figure 4 and 5) using field spectrometers are also proposed as they may assist in determining the nature of mineral alteration and vectors to ore body.

Figure 4: Close-up of
rhyolitic cobble showing porphyritic texture

Figure 5: Close-up of a boulder showing fine,
disseminated iron-stained sericitised matrix

Greendale Prospect

Cross-sections were generated from drillhole data supported by detailed photogeology, which was carried out to improve the current understanding of geology in this area. These new interpretations were integrated with the soil geochemistry and ground geophysics (IP and SP ground surveys) produced by previous explorers. This suggests that the mineralisation at Greendale is fault-related, open along the fault and at depth, and hosted by strongly silicified greywackes within a gently dipping Early Ordovician flysch sequence of alternating greywackes and shales. There is also an indication of a possible stratiform redox-type control to mineralisation.

Figure 6: GD7 drillhole log and an across fault drillhole section

Proposed Exploration Activities

Magnetic modelling of the Loaded Dog anomaly was completed which indicates the presence of several targets, allbeit at depth. Drill testing of these targets will be deferred for the time being. In the meantime, Richmond Mining is reassessing its program for this licence following the abandonment of its recent drilling program on the Mayfield Project to the south.