St George Mining identifies multiple strong EM conductors at Mt Alexander

by Leena Thomas
Image: St George Mining Limited

St George Mining Limited (ASX: SGQ) announced that the exploration at its flagship Mt Alexander Project in the north-eastern Goldfields in WA has detected two strong EM conductors.

The company announced that two very strong off-hole electromagnetic (EM) conductors – modelled with conductivity of 49,000 and 16,200 Siemens respectively –were identified by the downhole EM (DHEM) survey in MAD184. SGQ said that the new EM conductors were detected approximately 475m downhole in MAD184 and represent the deepest conductors ever identified at Mt Alexander.

The company reported that MAD184 was drilled at the West End Prospect, in an area with no prior drilling and more than 800m north-west of known massive sulphides in the Cathedrals Belt. SGQ said that the electrical signature of the new conductors is consistent with a massive sulphide source.

The company noted that all other EM conductors with similar characteristics in the Cathedrals Belt have been confirmed by drilling to be massive sulphides with high grades of nickel, copper, cobalt, and PGEs.

SGQ said that drilling of the new EM conductors is scheduled to commence early next week with outstanding potential to make a new discovery of massive sulphide mineralisation.

The company said that the new EM conductors further confirm the camp-scale potential of the +16km long Cathedrals Belt with four shallow high-grade nickel-copper sulphide deposits already discovered and new high priority targets being established. The company said that the DHEM surveys in other recently completed drill holes have also identified additional EM anomalies that are being assessed and prioritised for drill testing.

Mt Alexander project

The Mt Alexander Project is located 120km south-southwest of the Agnew-Wiluna Belt, which hosts numerous world-class nickel deposits. The Project comprises six granted exploration licences – E29/638, E29/548, E29/962, E29/954, E29/972, and E29/1041.

The Cathedrals, Stricklands, Investigators, and Radar nickel-copper-cobalt-PGE discoveries are located on E29/638, which is held in joint venture by St George Mining Limited (75%) and Western Areas Limited (25%). St George is the Manager of the Project, with Western Areas retaining a 25% non-contributing interest in the Project (in regard to E29/638 only) until there is a decision to mine.

Drilling at Mt Alexander

The company had recently commenced a drill programme at Mt Alexander focused on deeper drilling to test conductive features identified by a number of geophysical surveys completed by St George across the Cathedrals Belt.

SGQ said that the drill targets are located below and down-dip from the shallow high-grade deposits already discovered in the Belt.

MAD184 was completed to a downhole depth of 497.8m to test a broad single component (Z) EM anomaly identified by the surface SQUID MLEM survey carried out earlier this year. The drill hole intersected a 23.2m thick mafic-ultramafic unit from 444.5m downhole.

Four new drill holes

The company reported that a further four drill holes, MAD188, MAD189, MAD190, and MAD191 were completed since 9 September 2020. SGQ said that all the additional drill holes intersected varying thicknesses of intrusive-style rocks, confirming the very extensive target horizon for potential nickel-copper sulphide mineralisation. DHEM surveys of these new holes have yet to be completed.

The company reported that the results in the current drill programme have confirmed an extensive intrusive mineral system at the Cathedrals Belt with strong potential for additional massive sulphide deposits to be present below the shallow high-grade deposits already discovered.

DHEM survey reveals two prime targets

The company said that the DHEM surveys on the completed drill holes are being used to identify discrete EM conductors for follow-up drilling. The company said that the results in the current drill programme have confirmed an extensive intrusive mineral system at the Cathedrals Belt with strong potential for additional massive sulphide deposits to be present below the shallow high-grade deposits already discovered.

The company said that the DHEM survey in MAD184 recorded a very strong off-hole anomalous response to the east and down dip at 475m downhole. The response was seen in the mid to late times with a modelled conductivity of 49,000 Siemens, which is consistent with a massive sulphide source.

SGQ said that a second anomaly was detected to the northwest of the drill hole and has a modelled conductivity of 16,200 Siemens.

St George Mining noted that given the large distance of MAD184 from other drill holes, any potential high-grade mineralisation at this location is open in the direction beyond the anomalies.

The company said that the modelled plates for these new EM conductors are interpreted to represent the strongest part of the anomalous EM responses and are a reliable targeting tool to test for the presence of massive sulphides.

SGQ noted that the surface EM surveys completed over the MAD184 area did not detect the new strong DHEM conductors because of the conductive cover that extends west of Investigators and over West End, as well as the depth of these new conductors.

The company said that the survey recorded weak off-hole responses in holes MAD180, MAD181, MAD183, and MAD186. The hole MAD185 was blocked at 325m downhole and the survey could not be completed. There were no anomalous responses in the DHEM data for DD holes MAD182 and MAD187.

The company announced that the new DHEM conductors provide potential to significantly increase the footprint of known high-grade mineralisation in the large mineral system at the Cathedrals Belt.

What’s next?

St George Mining had paused the driling at Mt Alexander while DHEM surveys were completed.  The company said that diamond drilling is scheduled to resume this weekend with one diamond rig due to arrive at site by Friday.

SGQ said that the first hole to be drilled will test the 49,000 Siemens conductor identified from the DHEM survey in MAD184, followed by a hole to test the 16,200 Siemens conductor from MAD184. The company said that further holes will be planned based on the results from DHEM surveys in the new holes as well as in MAD185.

The company reported that further exploration will be planned based on ongoing drill results, geophysical surveys, and geological assessment of prospectivity.

Management comments

John Prineas, St George Mining’s Executive Chairman, said: “Our deep drill programme is delivering excellent results with thick intrusive-style rocks and nickel-copper sulphide mineralisation intersected at depths not previously explored.

The downhole EM surveys have delivered the breakthrough moment with two new exceptional conductors identified from MAD184 that are both interpreted to represent massive nickel-copper sulphides.

The MAD184 conductors are particularly exciting as they are the deepest conductors ever identified in the Cathedrals Belt and located 800m to the west of previously intersected massive sulphides on the Cathedrals Belt.

The potential discovery of massive sulphides at these new conductors could be our most important discovery to date as it would confirm the continuity of the high-grade mineralisation at depth and upgrade the western extension of the Cathedrals Belt – which covers the 2.5km long West End Prospect that straddles the major Ida Fault – as a fertile and highly prospective area for further mineralisation.

The Cathedrals Belt is interpreted to dip to the north-west at about 40 degrees so, from a geological perspective, the MAD184 conductors are in an ideal location for the presence of massive sulphide mineralisation down-dip from the high-grade mineralisation already discovered near surface.

With a 100% success rate in testing these kinds of conductors in the Cathedrals Belt, we are confident that our next significant discovery of massive nickel-copper sulphides is imminent.”