Westminster is in the process of closing on its newest acquisition, the Mostazal copper project in Northern Chile. Mostazal hosts an undrilled classic copper porphyry target along with significant high-grade copper-silver mineralization at surface. The company plans to prioritise the porphyry target but will also advance the identified stratabound mantos-style mineralization, which is reported as a historical drill-indicated resource. Recent pilot production of 120,000 tons grading 1.8% Cu was reported by a prior operator.*
Mostazal is located in the Atacama region of Chile, 80 kilometres northeast of Copiapo. The Atacama Desert is among the richest copper regions on earth, hosting some of the world’s most significant porphyry copper deposits. The property is situated within the 500-kilometre long, north-south trending Domeyko Fault System, the major structural control for the majority of Chile’s largest copper mines including Escondida (BHP, Rio Tinto), Chuquicamata and the El Salvador mine (Codelco). The El Salvador porphyry deposit is 40-kilometres north of Mostazal, at a similar elevation and longitude.
Mostazal presents at surface as a copper and silver stratified system in porphyritic andesites with lenses of mineralization or mantos. The mantos mineralization is interpreted to be the shallow expression of a hidden, deeper porphyry system interpreted by geophysics with a characteristic chargeability-high coincident with a magnetic-low. Mineralization occurs in an area of stacked and discontinuous stratified lenses measuring 2.5 km long by 2 km wide and up to 300 m deep. The supergene mineralization is malachite, azurite, chrysocolla, atacamite, hematite and limonite. The principal copper sulfide observed is chalcocite, disseminated in the rock matrix and as fine veinlets. Bornite, chalcopyrite and native copper have been identified.
An exploration program was undertaken in 2012 and 2013 by a previous operator. This work included detailed geological surveys, mapping, induced polarization (IP), ground magnetics surveys, and surface sampling of outcropped mineralization. In addition to the surface work, a drill program of 60 shallow diamond drill holes was completed over the two years for a total of 11,379 metres, targeting the extensions of the surficial mineralization indicated by the geophysical surveys. Summary work as follows:
- Induced polarization (IP) and ground magnetic surveys conducted with east-west lines spaced every 50 metres, for a total of 218 kilometers covering a grid of approximately 2.5 km by 5 km.
- Semi systematic geochemical survey oriented to the outcropping mineralization sectors and / or alteration, for a total of 123 samples.
- A 200 m x 200 m geochemical grid, covering a 2,500 ha area
- The collection of 550 chip and rock samples
- Drilling campaign of 60 diamond drill holes, totaling 11,379 m of drilling, which resulted in the collection of 6,283 samples for laboratory analysis
- Detailed Geological Mapping at 1:1000 scale in the Mostazal Prospect area. This included identifying lithological units, mineralization, and structures at the surface.
- Topographic survey of 1,400 hectares surface area covering the area of interest, with equidistant level curves of 5 to 1 m.
The 2012-2013 drilling prioritized exploration on the stratified lenses near surface expression. The completion of high quality induced polarization (IP) geophysical surveys identified new targets. The new IP targets to both the west and east of the known stratified lenses support the thesis that near-surface mineralization may be a distal expression of a much larger porphyry system at depth. This thesis will be central to Westminster’s target generation. The property has:
- Similar lithology and age as the nearby El Salvador Mine
- Associated with the Domeyko Fault System that immediately passes to the east
- Local Identified copper mineralization in an area of 5 kilometres by 3 kilometres
- Classic geophysics chargeability high – magnetic low porphyry signature underlying known copper mineralization
Westminster has engaged the services of Campbell & Walker Geophysics Ltd. to review existing geophysical data together with the historic drill hole database. This will then be integrated into Leapfrog geology software by Caracle Creek International Consulting Inc. to produce an updated three-dimensional model of the study area for future drill targets. Westminster has scheduled a drill program for Spring 2021 to drill test porphyry targets and assess potential for resource definition of near surface mantos copper mineralization.
* HISTORICAL MANTOS RESOURCE ESTIMATE:
In 2015, APGC Corp Chile SpA of Chile generated a resource estimate for Mostazal based on the 60-hole database and related geological information. They estimated an Indicated resource of 10 million tons grading 0.95% Cu and 8 g/t Ag, with a cut-off grade of 0.5% Cu and constrained to lenses more than 2 metres thick and less than 150 metres from surface.
It is unknown if the historical Indicated APGC estimate uses the current resource categories as defined by CIM; the differences to the CIM categories are not known. To upgrade and verify the historical Indicated estimate the Company would need to verify the historical drilling and engage the services of a professional resource estimator. The qualified person, Derrick Strickland, P. Geo. has not done sufficient work to classify the historical Indicated estimate as a current mineral resource. The Company is not treating any of the historical estimates as a current mineral resource.