Punta Alta
Location
The Punta Alta property consists of seven exploration concessions totaling 2,000 hectares and 100% owned by San Lorenzo. The Property is an early stage exploration property located eight kilometers north northwest of the historic Carrizal Alto copper-gold-cobalt mining camp in the Coastal Cordillera of Region III, Chile.
Regionally, it lies within the structural contact zone between the Devonian-Jurassic Metamorphic Terrain and the Jurassic-Cretaceous Intrusive Terrain of the Coastal IOCG/Cretaceous Porphyry Copper-Gold Belt. The same regional geological and structural environment as the historic San Roman, Carrizal Alto, Astillas, Pastos Largos and Cobaltera mining camps that were primarily active during the period 1820 – 1947 (Figure 1)
The Punta Alta Property is readily accessible from the town of Vallenar, 65 kilometres to the southeast, via paved and all-weather gravel roads to Carrizal Alto eight km SE of the Property. Several gravel roads heading generally north to northwest from Carrizal Alto to several old mines afford access to the interior of the Property.
REGIONAL STRUCTURAL & METALLOGENIC SETTING:
The Punta Alta property occurs within the southern Copiapó - Ovalle sector of the Chilean Coastal Iron Oxide Copper Gold (IOCG)/Cretaceous Porphyry Copper-Gold Metallogenic Belt in the Andean Pre-Cordillera of Regions III and IV, northern Chile.
The Copiapó - Ovalle sector of the Belt can be divided geologically into two NNE-SSW trending fault bounded sub-belts locally referred to as from W to E as the Coastal Metamorphic (Devonian-Jurassic), and the Coastal Intrusive - Volcanic (Jurassic-Cretaceous) Terrains (Figure 2).
Along the contact zone between the Coastal Metamorphic and Intrusive Terrains between Copiapó in the North and Ovalle in the south, high-grade copper-gold breccia vein and semi-massive sulphide deposits that are locally enriched in copper, gold, silver and cobalt in the range of 2 – 5 % copper, 5 – 20 g/t gold, 10 – 50 g/t silver and 0.2 – 6% cobalt are common.
The highest grades of copper, gold, silver and cobalt generally occur in both hydrothermally altered Jurassic andesitic metavolcanic and metasedimentary rocks and/or local Cretaceous dioritic intrusive and andesitic volcanic rocks proximal to or within NNE-SSW trending transcurrent faults such as the Freirina and La Serena Fault Zones.
The Freirina Fault Zone (¨FFZ¨) can be traced at least 250 km along strike from 50 km north of the San Ramon mining camp west of Copiapó to Bahia Carrizal in the south. Throughout its length the FFZ is host to historic mining camps such as Carrizal Alto and Cobaltera.
The La Serena Fault Zone (¨LFZ¨) likewise can be traced at least 425 km from where it diverges from the FFZ north of Sam Ramon to about 50 km south of Ovalle in the south. Along most of its length LFZ traverses the Chilean Coastal Iron Belt, the western most phase of the IOCG Belt best known for its magnetite deposits. However, many of these are associated iron-copper-gold-cobalt deposits.
This Eastern Intrusive Terrain is characterized by the presence of small <5 km2 porphyritic intrusions and subvolcanic rocks of dacite/granodiorite to diorite composition of Lower to Upper Cretaceous age associated with porphyry, skarn and high sulphidation vein copper, gold and silver deposits.
The Punta Alta property is located within a prime sector of the Freirina Fault Systems in the historic Carrizal Alto mining camp.
The past production + current reserves and resources of the main deposits in Copiapó - Ovalle sector of the Belt (Table 1) are over 37 billion pounds of copper and over 27 million ounces of gold divided between IOCG and intrusion-hosted porphyry-type deposits. .
PROPERTY GEOLOGY & MINERALIZATION:
The Punta Alta property is in a prime sector of the FFZ along known or inferred extensions of past producing high-grade Cu, Au and Co bearing veins systems like those found in the nearby Carrizal Alto mining camp (Figure 3).
The Punta Alta property claims overlie predominantly Jurassic to Cretaceous dioritic to monzodioritic intrusives locally in fault contact with Devonian to Permian aged schistose meta volcanic and meta sedimentary rocks. This rock package is part of the Coastal IOCG Belt Metamorphic and Volcanic-Intrusive Terrains and the dominantly NNE – NE tending faults that cut them are part of the regionally extensive FFZ.
The FFZ forms the NW boundary of the central block of Devonian to Permian aged schistose meta volcanic and metasedimentary rocks. It is host to a trend of Cu-Au-Co mines which extends NE for over 17 km from Dos Amigos through Mina Argentina, Fuego and Infiernillo to Punta Tagnia. At Minas Fuego and Infiernillo about halfway along the trend strong mineralized splay faults hosting calcite-quartz-sulphide breccia and shear veins and stockworks within wider silica-sericite-pyrite zones containing Cu, Au +/- Co, Ag mineralization head north across the center of the Punta Alta claim block. The veins encountered at the old mines on the Punta Alta property such as Lechuza are similar in alteration and mineralogy to Minas Grande and Armonia, the two principal producers at Carrizal Alto and vary in thickness from 2 - 8m.
Typically, the upper 50 - 150 metres of these vein systems in the Carrizal Alto camp are oxidized and judging from their remnants many of them were probably worked to just to the base of the oxides and abandoned as the sulfides were reached. The oxide mineralization as seen at the Lechuza mine on the Punta Alta property consists mainly of the copper oxides pseudomalachite, chrysocolla and copper wad. In the deeper mines at Carrizal Alto primary mineralization consists predominantly of chalcopyrite, pyrite and cobaltite plus minor pyrrhotite and gray cobalt (skutterudite/smaltite).
EXPLORATION HISTORY:
The Punta Alta property is proximal to the 19th century copper mining center of Carrizal Alto. Mining commenced at Carrizal Alto in the late 1820´s and continued at a significant scale, mostly by British companies, until 1891 when flooding closed the mines. During this period more than three million tons of ore grading more than 5% copper and 0.6 oz/ton gold over widths of 2 - 15 metres as well as several hundred thousand tons of direct shipping ore grading 12% copper and 1-2 oz/ton gold was extracted. Historical reports indicate that the larger mines were still in these ore grades over similar widths in the lowest, 480m deep workings at the time of the flooding.
* Readers are cautioned that historically reported mineral deposits and production results are not indicative of mineral deposits on the Company's property or any potential exploitation thereof. Readers are also cautioned that a "qualified person" (as defined by National Instrument 43-101) has not yet completed sufficient work to be able to verify the historical information, and therefore the information should not be relied upon. In September 2001 Vector Mining S.A., a Chilean private company conducted limited mine pillar and dump sampling at the Lechuza Mine assays from which are reported to have graded 1.5 – 3.2% copper, 2.7 – 12.1 g/t gold and 0.2 – 0.35% cobalt.
In April 2019, Minera San Lorenzo staff completed a limited program of reconnaissance level prospecting and rock sampling of pillars left in four of the old mines on the Punta Alta property including the Lechuza Mine. Assays from the 12 samples collected returned values in the range of 0.32 - 1.33% copper and 3.39 – 16.75 g/t gold and 0.1 – 0.15% cobalt over 1.0 - 1.5m widths.