The large La Curva gold project in Santa Cruz hosts multiple prospects along the six kilometers La Castora gold trend and additional prospects in the Curva West area. La Curva was staked in 2005 to secure alteration anomalies identified by Mirasol’s generative team. The La Curva project forms part of a newly recognized low sulphidation precious metal district within the prolific Deseado epithermal province which contains five operating multi-million ounce gold and silver mines. The project was under an option to joint venture with OceanaGold from May 2017 to March 2019.
During the La Curva option agreement (May, 2017 to March, 2019 ), OceanaGold has completed C$3.7 million in exploration expenditures on the project and drilled 6,250 m in 36 holes. In addition, OceanaGold has also made approximately C$400,000 in option payments to Mirasol.
Phase I drilling at the La Curva Castora Trend has provided an initial test of three prospects: Cerro Chato, Loma Arthur and SouthWest. This drilling campaign has intersected widespread pervasive argillic alteration, silicification and Gold+Silver mineralization indicative of a low-sulfidation epithermal gold system. Mineralization is developed as a series of veinlet zones within the structurally prepared welded ignimbrite wall rock, as disseminations within laminated water lain sediments and as matrix fill in phreatomagmatic and dome margin autobreccia bodies. Preliminary geological interpretation suggests the Castora Trend prospects represent a series of intrusive dome related maar diatreme breccias.
Assay results from Phase I drilling confirm the presence of a large Gold+Silver system within the Castora Trend with broad zones of anomalous Gold+Silver intersected including:
47.9 m at 0.48 g/t Au and 2.1 g/t Ag (CC-DDH-01)
106.2 m at 0.61 g/t Au and 2.7 g/t Ag (SW-DDH-02)
The better down hole intersections at 0.3 AuEq60*g/t cut off include:
19.65 m grading 0.72 g/t Au and 2.6 g/t Ag, including 0.80 m grading 6.12 g/t Au and 18.6 g/t Ag, and 5.75 m grading 1.24 g/t Au and 2.0 g/t Ag, including 0.85 m grading 5.99 g/t Au and 5.9 g/t Ag (CC-DDH-01).
13.00 m grading 1.22 g/t Au and 0.7 g/t Ag, including 7.4 m grading 1.81 g/t Au and 0.7 g/t Ag (LA-DDH-04).
6.20 m grading 2.33 g/t Au and 31.1 g/t Ag, including 1.80 m grading 6.88 g/t Au and 84.9 g/t Ag, and 26.7 m grading 0.82 g/t Au and 2.2 g/t Ag, including 1.45 m grading 3.50 g/t Au and 11.3 g/t Ag (SW-DDH-02).
Two distinct stages of gold mineralization are recognized:
Stage 1: This stage is characterized by broad zones (up to 106.2 m downhole) of lower-grade, early quartz-pyrite.
Stage 2: This is a later, overprinting phase of higher-grade multi-pulse epithermal veins and veinlets with individual assays up to 0.8 m grading 12.72 g/t Au and 145.4 g/t Ag (SW-DDH-02).
The Phase II program of diamond core and reverse circulation drilling completed in late 2018 at the project, totalled 3,227.8m in 17 holes, testing targets at the Curva West prospect and the Castora Trend’s Cerro Chato, SouthWest and Pison prospects (Figure). Encouraging anomalous gold+silver intersections were returned at the 3 Castora Trend Prospects, with best results received from SouthWest drill holes SW-DDH-08,09 and SW-RC-01, and Cerro Chato drill hole CC-DDH-010 (Table):
SW-DDH-08: 20.0 m at 0.97 g/t Au and 1.9 g/t Ag,
Including, 5.50 m at 2.11 g/t Au and 4.3 g/t Ag
SW-DDH-09: 135.6 m at 0.54 g/t Au and 3.8 g/t Ag,
Including, 0.60 m at 12.95 g/t Au and 220.0 g/t Ag,
5.40 m at 1.55 g/t Au and 10.4 g/t Ag, and
1.05 m at 10.72 g/t Au and 60.0 g/t Ag
SW-RC-01: 60.0m at 0.43 g/t Au and 6.6 g/t Ag,
Including, 3.0m at 3.62 g/t Au and 54.3 g/t Ag
CC-DDH-010: 26.3m at 0.56 g/t Au and 10.7 g/t Ag
Including, 0.45 m at 24.1 g/t Au and 87.3 g/t Ag
Results from all drilling to date and surface geology at SouthWest, outline a NW oriented 1,100 m long and up to 300 m wide target zone for Au+Ag mineralization. Cross sections through this target, show Au+Ag grades vectors to depth and the north, toward a large NW striking normal fault that may have acted as a “feeder structure” to mineralization. This structure represents a compelling drill target for higher grade Au+Ag mineralization (Figure and Figure).
Nine samples weighing up to 1 kg, composited from mineralized drill assay pulps from the SouthWest and Cerro Chato prospects, were assayed via the LeachWELLTM process, as an initial test of cyanide recoverable gold characteristics of the main styles of mineralization recognized to date (Table). Encouraging gold recoveries were received from the SouthWest prospect with 93.9 % gold recovery achieved from banded epithermal vein style mineralization and an average 69.5% from Mineralization Style 2, breccia matrix mineralization (with an average of 73.6% recovery from all samples for the prospect). The banded epithermal vein style mineralization at Cerro Chato returned a gold recovery of 98.58%, however recoveries for Style 1 sulfide veinlet and breccia matrix mineralization were much lower at the Cerro Chato prospect, averaging 26.2%.
Petrographic analysis of the different styles of mineralization confirm free gold and ruby silver (proustite – pyrargyrite) are consistently present in the banded vein mineralization at Cerro Chato and SouthWest, and also present in the Style 2 breccia matrix mineralization at SouthWest, correlating with the samples showing better cyanide leachable gold recovery. Further exploration at La Curva will be directed toward drill targets where these metallurgically more favourable styles of mineralization are dominant.
Additional Explanatory Notes: * AuEq60 is the sum of the value of gold and silver in a given interval represented as a gold equivalent g/t value calculated via the formula: Au assay in g/t + (silver assay in g/t ÷ 60)