The Primavera gold-copper porphyry project is located 7 kilometres south of the historic Santa Rita copper-gold skarn mine and is located within the southern portion of the Calibre-B2 JV concession area. The project is road accessible and is located 1.2 kilometres from the national power grid and is 8 kilometres south of the town of Rosita.
Primavera is located within a 5 kilometre by 7 kilometre area dominated by Tertiary volcanics and early Cretaceous aged calcareous sediments which have been intruded by multi-phase intermediate dikes and diorite intrusive rocks. Quartz veins have also been mapped on the property. The prospect area contains coincident gravity, magnetic and radiometric anomalies identified by various airborne geophysical surveys, which are believed to be related to a large underlying intrusive centre. The area is prospective for porphyry, skarn and epithermal vein deposit types.
In the Primavera main zone, drilling has focused on testing the strike and depth continuity of high grade Au-Cu mineralization intersecting wide intervals of porphyry style mineralization to depths of 250 metres. The drilling has been centered on a 250 metre x 350 metre area with subsequent step out drilling following the mineralization to the west-southwest. Major north-northeast and west-northwest oriented faults control and cut the mineralization in the main zone at Primavera. Drilling across these structures intersected porphyry style mineralization but has not yet located the offset portion of the higher grade zone.
The main zone shows classic porphyry stockwork mineralization consisting of millimeter to centimeter scale quartz-pyrite-chalcopyrite-bornite-magnetite veins associated with potassic alteration of the host rock. Individual veins and quartz stockwork show a preferred northeast orientation in the southern portion of the zone but become dominantly northwest oriented in the northern zone.
The highest grades in drilling are associated with strong potassic alteration in the form of K-spar in diorite and secondary biotite in the andesite porphyry. Bornite is also commonly found in these zones. Multi-stage quartz veining indicates that the earliest mineralization predates intrusion of the diorite as the diorite unit cuts both the andesite porphyry and earliest quartz veins. “Ore grade” mineralization is hosted in both the andesite porphyry and later diorite.
A total of 13,413 metres has been completed at Primavera in 32 drill holes. Highlights of the drilling are shown in the table below. The results from preliminary metallurgical testing have also been included.
*AuEq (g/t) Gold Equivalent calculated using 1,300/oz gold and 43.00/lb copper and metallurgical recoveries and net smelter returns are assumed to be 100%
**No significant values
2017 - 2018 Drilling Program Underway
The 2017-2018 drilling program at Primavera has begun and will test a series of high priority targets in two areas within the overall Primavera Gold-Copper Porphyry District;
- NE Trend (2km x 1km area) extending northeast from the existing deposit, and
- San Francisco Target (2km x 2km area) centered three kilometres southeast of the Primavera deposit.
This is the first drilling program at Primavera since 2012 and will consist of approximately 45 Reverse Circulation drill holes totaling 8200 metres. Drilling will in part be guided by a series of recommendations made by Dr. Richard Sillitoe, one of the world’s foremost porphyry experts, following his site visit and evaluation in February 2017. Numerous high priority drill targets prospective for further gold-copper porphyry mineralization exist within the 5.0 kilometre by 4.0 kilometre Primavera target area as defined by anomalous gold and copper in rock and soil samples, magnetic and radiometric geophysical anomalies, and targets where geological mapping has identified porphyry style mineralization or alteration.
In a report entitled “An Investigation into Scoping Level Testwork on Primavera Project Samples” dated February 8th, 2013 by SGS Canada Inc. of North Vancouver (“SGS Canada”) four composite samples of Primavera porphyry mineralization from drill hole PR-012-16 (201.35 m grading 0.77 g/t Au and 0.36% Cu) were submitted for initial metallurgical studies. Sample head assays are outlined in Table 1. Individual sample weights ranged from 18.6 kg to 30.3 kg. The metallurgical tests conducted on the Primavera project samples included rougher flotation kinetic and cleaner flotation tests and whole ore cyanide leach tests.
Summary of Head Assays
In optimized rougher flotation tests on the four Primavera samples gold recoveries ranged from 86% to 91% and copper recoveries ranged from 94% to 98%. Initial metallurgical tests indicate that the recovery of gold, copper and sulphur are strongly related to each other and recovering sulphur by flotation will recover most of the copper and gold. Two different grind sizes were tested during the study with the finer grind returning the best recoveries. Additionally, whole ore leach tests on the four Primavera samples extracted 90.0% to 96.6% of the gold using 1.2 kg/t to 2.43 kg/t of NaCN. Gold kinetics on the leach tests are moderately fast reaching plateau within 30 hours and gold in all leach tests exhibited free milling qualities.