Status: Available for Option
Los Cuarentas is a low sulfidation epithermal Au+Ag target characterized by strong argillic and phyllic alteration surrounding low sulfidation epithermal vein systems that host gold and silver mineralization. Vein textures and silica polymorphs suggest that the higher levels of the epithermal systems are present throughout the under-explored district. Hydrothermal alteration is overprinted in places by strong oxidation after pyrite and other sulfides. Several target zones have been identified and most are ready for drilling; these are named: Santa Rosalia, Santa Rosalia Sur, El Sombrero and El Chapo.
Location and Setting
The property is located in northern Sonora, 170 km northeast of Hermosillo near the El Mercedes mine (operated by Premier Gold Mines) and the Las Chispas epithermal gold project (operated by Silvercrest).
The mining concessions total 807 has and include Los Cuarentas Fracc II (Title 24430) with 720.26 Ha and Santa Rosalia centered on the historic Santa Rosalia Mine (Title 1976926) with 87.74 Ha.
Historic Spanish workings exist on the property in an east-west striking epithermal quartz vein system from which gold was historically mined. Work by previous claim owners included three drill holes. These holes did not test the targets identified today. The nearby Mercedes vein was discovered in 1936. Las Chispas, only 20 km southeast of Los Cuarentas, contains high grade silver-gold veins that are actively being explored.
Geology and Mineralization
Lower Cretaceous Bisbee group limestones are the oldest mineralized rocks, but most of the area is covered by upper Cretaceous volcanic conglomerates, andesite agglomerate, and younger rhyolites which are the preferred host to mineralization. All units are cut by Tertiary monzonite. Structures associated with the east-west oriented historically-mined Santa Rosalia deposit are a result of a large fissure fault. Northwest trending shears that produced the fissure have also produced northwest trending structurally controlled mineralization hosted in Oligocene low sulfidation quartz-carbonate veins with economic Au and Ag. Some veins at Los Cuarentas occur entirely within an andesite flow breccia and in one location (Santa Rosalia) veins containing mineralization are located at a fault contact between andesite and rhyolite.
Textures observed are typical of a low sulfidation epithermal system and include: presence of incipient banded quartz, quartz breccia, silica after calcite (bladed) and quartz veinlet arrays inside fault breccia and gouge. Mineralization is found as banded crystalline to cryptocrystalline quartz and calcite bearing minor chalcopyrite and galena, sulfosalts, and pyrite. Silver may be present as acanthite and argentite minerals.
Light-colored to reddish alteration zones are widely distributed at Los Cuarentas. At outcrop scale the area contains goethite that stains and fills cracks, white mica (sericite and Illite) and minor amounts of hematite after pyrite, forming argillic alteration packages. Spectroscopy studies on rock samples outline an advanced argillic zone with alunite at El Sombrero. Advanced argillic points defined by dickite±pyrophyllite ±kaolinite assemblages form a cluster at Santa Rosalia Sur. Pervasive to patchy silicification is observed at Santa Rosalia, Santa Rosalia Sur and El Sombrero.
Recommendations include: Detailed geologic mapping with rock sampling over the entire Santa Rosalia claim to better define structural controls and alteration associated with the Ag-Au mineralization, an expansion of the current soil and rock grids to define mineralized bodies on or near the surface, drilling at Santa Rosalia Sur and Santa Rosalia and geologic mapping and sampling at the lesser developed El Sombrero and El Chapo prospects.
Agreement and Terms
Millrock has 100% ownership of most of the property, and an option to purchase a 100% interest in the small internal claim covering the historic Santa Rosalia mine. Sandstorm Gold Ltd. holds a 1.5% royalty on a portion of the property.
“THE TECHNICAL INFORMATION WITHIN THIS DOCUMENT HAS BEEN REVIEWED AND APPROVED BY GREGORY A. BEISCHER, PRESIDENT & CEO OF MILLROCK RESOURCES INC. MR. BEISCHER IS A QUALIFIED PERSON AS DEFINED IN NI 43-101.”