GEOPHYSICAL SURVEY UPDATE FOR THE PERRINVALE VHMS PROJECT
Downhole EM Identifies Priority Drill Targets at Perrinvale
- Down hole electromagnetic surveys have been undertaken on the recently completed diamond core drill holes at the Schwabe, Zinco Lago and Monti Prospects, plus two of the reverse circulation holes drilled in 2019.
- A number of promising electromagnetic conductors have been identified within the Perrinvale Project including: the existing Schwabe drill area; below recent drilling at Zinco Lago; off hole along the Zinco Lago - Lago Rame gossan trend; and adjacent to the recent Monti drilling.
- Ground electromagnetic surveys now underway to further refine targets for the next phase of drilling at the Perrinvale Project.
DHEM surveys were undertaken on the diamond core drill holes recently completed at the Schwabe, Zinco Lago and Monti Prospects, plus two of the reverse circulation (RC) holes drilled in 2019 (located southwest of Schwabe and along the gossan trend south of Zinco Lago). This data has been reviewed in conjunction with the broad spaced Moving Loop Electromagnetic (MLEM) and Airborne Electromagnetic (AEM) surveys completed in 2019.
The DHEM survey at the Schwabe Prospect aligns well with the model of the 2019 AEM survey, indicating a robust and highly conductive core area within the existing exploration area, and some potential for a lower conductivity zone extending to the north or north-northwest of existing drilling. A MLEM survey is currently underway at Schwabe to further refine the next phase of drilling of the VHMS mineralisation previously identified at this location (refer to ASX announcement 16/04/2020: Significant High-Grade Copper Gold Results at Perrinvale).
Zinco Lago Prospect
The DHEM surveys of the Zinco Lago diamond drill holes indicate a strong (6,000 to 7,000 Siemens) late time conductor below the drill holes which is not obvious in the AEM data. The spatial position of the modelled conductor is aligned with the down dip projection of the mineralised horizon identified in the Zinco Lago drill core (refer Figure 1*). The Maxwell model of this conductor strikes roughly north-south and is open to the limits of the data. The nature of the conductor response is indicative of a massive sulphide or highly graphitic lithology. While further exploration drilling is required to confirm the cause of conductance at the Zinco Largo Prospect, the Company is very encouraged by the primary sulphides including pyrite, pyrrhotite and chalcopyrite as veinlet and narrow (10-30cm) massive zones identified in the recent diamond core holes above this conductor.
Zinco Lago - Lago Rame Gossan trend
RC hole 19PVRC004 drilled in 2019, located along the Zinco Lago - Lago Rame gossan trend, 900 metres south of the Zinco Lago diamond drilling, was included in the DHEM surveys. The survey results generated off hole conductance, along with a very small on hole conductor associated with a narrow graphitic shale.
Two conductor plates have been modelled as shown in Figure 2*, including the RC drill trace. The best model fit generates a relatively flat mid time conductor and a deeper west dipping strong (6,000 to 7,000 Siemens) late time conductor. As for Zinco Lago, the strong late time conductor is considered indicative of a massive sulphide or highly graphitic lithology. The area has been revisited on the ground, with small scale folding noted in sub-crop within the sedimentary sequence. Folding on a larger scale may explain the orientations of the conductor models.
At the Monti Prospect, DHEM was completed in the north and south, with small conductive features identified in the north. In the south, a much stronger (6,000 to 7,000 Siemens) off hole conductor has been identified north east of diamond hole 20MTDD003, as shown along with recent drill results on Figure 3*.
Moving Loop EM Survey Underway
The Company has now commenced a program of ground electromagnetic (MLEM) surveys across the Perrinvale Project area. The MLEM surveys will encompass both recently drilled prospects and priority conductive features identified during the 2019 interpretation of the AEM data. Field truthing of these priority conductive features has recently been completed, prior to the MLEM survey design.
The broad objectives of the MLEM program include:
- to assess the potential for deeper conductors associated with the Schwabe VHMS system;
- further assessment of areas where DHEM conductors may be open or are yet to generate clear models; and
- improve resolution of other priority conductors noted in the 2019 AEM survey.
A review of all data, including geophysics (magnetics & EM), geological mapping and drill hole logging, has led to the design of MLEM surveys across eight areas (refer Figure 4*). The MLEM surveys, which typically have much greater depth penetration, have been designed to better assess potential deeper conductors, as well as to improve confidence in conductor models generated from AEM and DHEM data. At the completion of the MLEM surveys, the next phase of exploration drilling will be refined. This phase of drilling will include a mix of both RC (for shallower targets) and diamond core drilling (for deeper targets).
Exploration Program Moving Forward
The MLEM data is expected to be received progressively over the next 3 weeks of the survey period, allowing refinement of targets and finalisation of drill hole design. For most of the conductors being investigated, the existing Program of Works approvals will allow for immediate drilling.
Cobre's Executive Chairman and Managing Director, Martin Holland, said in relation to the recent EM results at the Perrinvale Project:
"The recent down hole EM results follows the positive diamond drill results reported recently at the Perrinvale Project. In particular, the off hole conductor along the Zinco Lago - Lago Rame gossan is an exciting new prospect identified by our exploration team. All together, these EM results provide encouragement to continue Cobre's systematic plan of utilising geophysics to refine drill targets in favourable geological positions across the Perrinvale Project area. I am encouraged in knowing our work to date has focused on a small part of the total project area. The 2019 AEM survey covered about 30% of our tenure and this current program is focused on a fraction of that survey area. I look forward to updating the market on the MLEM results as they become available and to leveraging the knowledge we gain to unlock potential across the entire project.
*To view tables and figures, please visit:
About Cobre Limited
Cobre Limited (ASX:CBE) is a Sydney based company focused on mineral exploration in Western Australia. The company recently discovered a new high grade VMS deposit enriched in Copper, Gold, Zinc and Silver in Western Australia from its maiden drill program in June 2019.