Tres Cruces Geology
New Oroperu’s 100% owned Tres Cruces property is located within a NW-SE trending belt of Paleogene volcanic rocks of predominantly andesitic composition called the Calipuy Volcanics. This volcanic belt trends from central to northern Peru and hosts world-class deposits like Newmont & Buenaventura’s Yanacocha Mine and Barrick’s Pierina Mine. The Tres Cruces property lies near the heart of the Quiruvilca mining district, which includes the Quiruvilca copper-lead-zinc-silver vein systems. Precious metal deposits in the area include the Lagunas Norte mine, an epithermal gold deposit which has produced over 10 million ounces of gold and has current resources of 4.3 million ounces (Barrick Annual Report 2020).
The Calipuy volcanic package overlies a Cretaceous sedimentary sequence (Chimu Formation) of quartz arenite and mudstone that shows a strong degree of deformation resulting from early Cenozoic SW-NE compression. This was later followed by E-W extension allowing loci of volcanic activity to develop. The Quiruvilca District is host to several mineral deposits all classified as epithermal type including Barrick’s Laguna Norte located 10 km north-northeast of Tres Cruces is classified as a high sulfidation system. Tres Cruces is considered to be of the low to intermediate sulfidation epithermal type. Age dating at Tres Cruces indicated the age of mineralization to be between 22-25 million years. This is older than the nearby Quiruvilca intrusive rocks hosting vein mineralization and the age dated alteration at Lagunas Norte.
Gold mineralization at Tres Cruces is hosted by a bimodal suite of andesitic to rhyolitic flows, domes, breccias, and volcaniclastics. Gold occurs with a fine grained dark arsenical pyrite, generally disseminated within its volcanic host, along structural zones and lithologic contacts. Accompanying the pyrite, trace amounts of associated minerals include marcasite, arsenopyrite, galena, stibnite, realgar, orpiment and enargite. Silver shows a moderate correlation with gold at a ratio of about 3:1. The gold is extremely fine, with over 95% having a diameter of less than 5μ. Rare coarse visible gold occurs in quartz veinlets. Oxidation of the gold mineralization has occurred from a few meters up to 100 meters below surface, developed primarily in rhyolitic host rocks.
Deposit Type and Alteration
The Tres Cruces property hosts gold deposits that have characteristics of a low- to moderate-sulfidation type epithermal system. Hydrothermal alteration in the core of the Tres Cruces deposit is dominated by illite with chalcedonic quartz, kaolinite, and smectite in the upper part. At depth, illite alteration is dominant with minor quartz and sericite. Geochemically, the gold mineralization is associated with arsenic, and at high levels, mercury.
Figure 1-1 below is a plan map of the geological lithologies at Tres Cruces. The figure also identifies the proposed pit outline for oxide and sulfide mineralization in the solid blue and red lines respectively.
Summary of Select Drill Holes With Oxide Mineralization
|Drill Hole||From (m)||To (m)||Interval (m)||Au (g/t)|
Figure 1-2 identifies the proposed pit outline as well as part of the Tres Cruces project boundary. The map also outlines the proposed Oxide Pit-outline as well as the Sulphide pit outline in the solid blue and red lines respectively. Figure 1-2 also includes multiple cross sections identified by the solid black line including sections 1990N, 2440N as well as section 101. Each of these cross sections below demonstrates the mineralization in each hole with gold grades in grams per tonne.
Main Oxide Pit Geology and Gold Graphs, Section 2440N, Viewed Looking North
Main Oxide Pit Geology and Gold Graphs Section 1990N, Viewed Looking North
Pit Block Grade Gold Cross-Section 101 looking Northeast
Section 101 looking northwest demonstrates the oxide zones (red line), leachable sulphides (light blue line) as well as the sulphide mineralization in the main proposed open pit. The proposed pit is outlined in black and demonstrates the estimated resources which are 100% pit constrained.
Pit Block Grade Gold Long-Section Row 124 looking Northwest
Metallurgical test work has indicated a baseline recovery of about 82% or better of the contained gold for heap leaching of oxide mineralization, and 65% for heap leaching low sulfide content mineralization. For the balance of the sulfides, 88% recovery is expected from test work using flotation followed by pressure oxidation and carbon in leach (“CIL”).
Gold recoveries do not necessarily depend on sulfur content. Those samples with both high gold recovery and sulphur content are primarily derived from shallower depths while those with high sulphur and lower recoveries are from deeper intervals. It is probable that in those samples exhibiting higher recoveries, some of the sulfur occurs in sulfate minerals (oxide state) versus sulfides. Those higher recovery sulfides from the upper reaches of the deposit that have lower sulfur content may have been partially leached of sulfur following oxidation, or the gold may deport as free grains. Some of this mineralization may be treatable by heap leaching or other low-cost recovery techniques.
No estimate has been made by the NI 43-101 Technical Report authors for silver although significant potential for value may exist at current silver prices. Indications are that silver grades are generally low and concentrated mainly in the deeper, sulfide portion of the gold deposit. Based on this updated gold resource scenario, overall silver grades would be expected to range between 1.5 and 2.5 g/t, potentially containing 2.5 to 3.5 million ounces of silver. If silver recovery can be achieved cost-effectively, overall project economics would be enhanced.
Property Description and Location
The Tres Cruces project is located in north central Peru about 100 km east of the city of Trujillo, a major city located 574 km north west of Lima (Figure 2 1). From Trujillo, the project is accessed by 127 km of paved highway. The Tres Cruces property consists of four mineral concessions totaling 3,000 ha located in the eastern part of the western Cordillera of north central Peru (Figure 2 2).
The Tres Cruces property is accessed from Trujillo by paved highway and a short gravel road. From Trujillo the trip to the property takes about 3 hours driving time. This main road accessing the Project from Trujillo was upgraded in 2004 during the construction phase of Barrick’s Lagunas Norte project. Subsequently, there has been significant additional road upgrading including major re-routing and paving. There is also an airstrip that services Barrick’s Lagunas Norte operation, which is located about 5 km north of the Project.
Barrick invested an estimated $340 million in the development of the Lagunas Norte deposit, which began production in June 2005. Barrick continuously mined the oxide part of the deposit as a heap leach operation until 2019, having produced 10 million ounces of gold, when the operation was put on care and maintenance having exhausted the near surface oxide portion of the deposit. Barrick is currently studying the feasibility of resuming mining of the sulfide portions of the deposit, as well as evaluating the possibility of mining other nearby mineralized areas to feed the Lagunas Norte operation.
The Tres Cruces property ranges in elevation between 3900 and 4200 m above sea level. The terrain is of moderate relief and the slopes in the Tres Cruces area are typically covered with low brush and grasses. Nearby, at lower elevations (<3500 meters) there is abundant agricultural activity typical of the Andes.
History of the Tres Cruces Project
There has been over 72,000 metres of drilling completed on the Tres Cruces project from all drill programs carried out on the property. Following the gold discovery at Tres Cruces*, drilling was completed by New Oroperu and subsequent joint venture parties. The last drilling completed on the Tres Cruces project was done by Barrick in 2008.
Mining activity has been ongoing in the region since the 1920’s, when Compañía Minera Quiruvilca started mining high-grade Pb-Zn-Ag veins at Quiruvilca, a small mining town 4 km west of Tres Cruces. In 1996 New Oroperu acquired the key concessions of the Tres Cruces property and entered into a 50-50 joint venture with Pan American on a combined land package, including adjoining ground held by Pan American that covered portions of the Tres Cruces mineralization. Drill campaigns utilizing reverse circulation (RC) and diamond drilling equipment were conducted by New Oroperu in 1996 and 1997, completing 61 drill holes, and later by Battle Mountain Gold in 1998 and 1999. Battle Mountain Gold relinquished their option of the Project in 1999 after drilling 80 diamond core holes and 26 RC holes.
In May 2002, New Oroperu entered into an agreement to acquire Pan American’s 50% interest to increase its interest to 100%, subject to a 1.5% royalty. Concurrently, New Oroperu entered into an agreement with Minera Barrick Misquichilca S.A. (Barrick), the Peruvian subsidiary of Barrick Gold, that would further the exploration of the Project. In September 2003, the agreement with Barrick was finalized and a definitive option agreement was signed. In October 2003, New Oroperu finalized their agreement with Pan American regarding their interest in the Project, effectively acquiring 100% of Tres Cruces through issuance of New Oroperu shares and the granting a 1.5% NSR royalty to Pan American.
The Barrick exploration program began with geological mapping, re-logging of existing drill core, and Induced Polarization (IP) and gravity geophysical studies. Barrick managed exploration and technical work competed on Tres Cruces project from 2002. Barrick drilled 202 holes on the project which includes a combination of RC drilling and diamond core holes with the last drilling completed in 2008. The only additional work carried out on the project was metallurgical test work completed in 2011.
*In summary, Tres Cruces was a grass-roots discovery made by New Oroperu in 1995 and drilled the discovery holes in 1996. New Oroperu completed 61 drill holes by the end of 1997. Battle Mountain Canada Ltd. (BMC) optioned the Property and completed an additional 106 drill holes in 1998 and 1999. Barrick Gold Corporation, through its Peruvian operating subsidiary, Minera Barrick Misquichilca S.A. (Barrick), advanced the Project under an option agreement with New Oroperu by drilling an additional 202 drill holes from 2002 to 2008 and completing geotechnical and metallurgical studies. The results of these drill campaigns are contained in the NI 43-101 Technical Report dated February 1, 2021 by Jeffrey D. Rowe, James N. Gray, and Ruperto Castro.