Enter your name and email to Receive Updates
The Covas property is located in the northwestern corner of Portugal. Tungsten mineralization is contained in a 3 km x 2 km ring of pyrrhotite-bearing skarn deposits surrounding a presumed buried multiple-intrusion complex. Some of the deposits were previously exploited by two Portuguese companies between 1949 and the early 1980’s. Union Carbide and several other companies explored the district extensively up through the mid-1980’s, resulting in approximately 27,000 meters of drilling in 329 holes. However, exploration was not systematic, and only an estimated 40% of the skarn zone was drilled. The central intrusion complex was not at all explored, and there remains a potentially large, bulk-tonnage porphyry tungsten target inside the skarn ring. From the reported drilling, surface trenching, and geological mapping, Union Carbide calculated a mineral resource (non NI 43-101 compliant) of 922,900 metric tonnes of 0.78% WO3 (tungsten trioxide) in the skarn deposits.
After three rounds of drilling, funded by partner Blackheath Resources, more of the skarn zone has been tested, particularly on the eastern side of the Covas Dome along the Castelo-Boundary-Cerdeirinha-Muito Seco-Lapa Grande band of tungsten deposits. Drilling also tested the Telheira deposit on the west side of the Covas Dome. There is still potential exploration to be done at the northwest end of the Dome and Skarn Ring, as well as along the whole southwest side of the Dome.
“Blue sky” potential lies in the central part of the Dome, which still has not been explored. The so-called Banda Azul, an east-west trending zone of negative magnetics anomalism and positive chargeability zones, is spatially related to strong greissen alteration and anomalous pathfinder elements gold, arsenic, antimony, and molybdenum in soil geochemistry, as shown in the figure below.
The conceptual cross section below gives an idea of the potential for a bulk-tonnage, low grade WO3 target in the Banda Azul zone. Proposal for drill holes would target a potentially mineralize cupola zone lying above the multiple-intrusion complex.
In early Q2 2015, Covas JV partner Blackheath Resources Inc. completed a maiden tungsten resource estimate. Following is a summary of their results, as compiled in an Avrupa Minerals news release, dated April 1, 2015.
“The Covas Tungsten Project, which consists of seven separate deposits in close proximity, is estimated to contain:
- 449,800 MTUs WO3 indicated mineral resource based on 1,081,000 tonnes at an average grade of 0.42% WO3
- 767,100 MTUs WO3 inferred mineral resource based on 2,211,000 tonnes at an average grade of 0.35% WO3
The current indicated and inferred mineral resources are stated using a cut-off grade of 0.10%. 19 total drill holes had interval grades capped to a lower average grade, allowing for a more conservative average grade. The price of tungsten is currently approximately $270 per metric tonne unit (MTU) (10kg) of contained tungsten trioxide (WO3).”
Again, quoting Blackheath, “highlights of the resource estimate include:
- Substantial increase in MTUs over previous historical estimates
- Shallow depth. Over 80% of the resource is located within 60 metres of surface
- Mineralization remains open in multiple directions including high-grade potential areas that will be tested during the next drill campaign focussing on resource growth and grade increase
- Higher grade resource using a 0.25% WO3 cut-off
- 375,200 MTUs WO3 indicated based on 686,000 tonnes at an average grade of 0.55% WO3, and
- 584,900 MTUs WO3 inferred based on 1,281,000 tonnes at an average grade of 0.46% WO3.”
Avrupa completed a basic geochemical study of the central zone. Analytical results from the 300-sample grid soil survey over the granitic intrusion complex, called the Covas Dome, were positive for tungsten, gold, arsenic, bismuth, and other metals. These results generally defined areas of immediate further interest within the Covas Dome, as shown by the following anomaly maps (Figures 1 through 6). Note that the better tungsten values occur in the SE half of the Dome, while gold is more preferential to the west and west-central portions of the dome. Strong arsenic anomalies are related spatially to both gold and tungsten, and bismuth anomalies are more closely related to areas of anomalous tungsten. Weak molybdenum anomalies cover the entire dome area, and weak tellurium anomalies occupy the central portions of the Covas Dome, partially coincident with the gold anomalies. The geochemical signature indicates potential for further tungsten mineralization, and also the possibility for reduced intrusion-related gold mineralization.
Recon geophysics and geological mapping
A predecessor company to Avrupa completed a prospect-wide grid magnetic survey in 2009-2010. Avrupa decided to re-process that data with the idea to better define the shapes of the potential skarn targets, as well as to better define structural controls to mineralization. The following two maps illustrate possible structural controls to mineralization, as well as the relation of magnetic highs around the skarn ring to already-known tungsten skarn deposits. In Figure 7, the tungsten soil anomaly in the Covas Dome is spatially related to a zone of strong magnetism, and known tungsten mineralization in the Skarn Ring is clearly spatially related to strong magnetic highs. However, anomalous gold in soils in Figure 8 is more closely related to strong east-west linears and general magnetic lows. Previously, the presence of gold in the Covas system had not been recognized. However, now it appears that there may be potential for both gold and tungsten mineralization in the Covas Dome area.
The company is now in process of field follow-up of the anomalies and definitive drill targeting in the Dome area, as well as selective targeting in the Skarn Ring zone. Previous mapping and prospecting in 2009 defined some relationships between structures, alteration, and possibility of mineralization. Field studies are presently building on that initial mapping and the recently-completed geochemistry and geophysics work. Avrupa expects to consolidate and prioritize drill targets before the end of the second quarter, in anticipation of first-pass scout drilling during the fourth quarter of 2011.