The La India mine is located approximately 200 km east of Hermosillo in Sonora, Mexico. The 629-square-km property includes the La India mine site, the Chipriona gold resource and several other prospective exploration targets situated in the prolific Mulatos gold belt.
The La India mine hosts proven and probable mineral reserves of 157,000 ounces of gold and 765,000 ounces of silver (7.3 million tonnes grading 0.67 g/t gold and 3.24 g/t silver) as of December 31, 2021.
The Chipriona open pit, polymetallic deposit on the La India property hosts indicated mineral resources of 260,000 ounces of gold, 18.0 million ounces of silver and 34,000 tonnes of zinc (6.4 million tonnes grading 1.26 g/t gold, 87.30 g/t silver and 0.53% zinc) and inferred mineral resources of 130,000 ounces of gold, 19.3 million ounces of silver and 37,000 tonnes of zinc (7.0 million tonnes grading 0.58 g/t gold, 85.75 g/t silver and 0.53% zinc) as of December 31, 2021.
Internal studies are ongoing to evaluate the potential to develop Chipriona, which is 1 kilometre north of the La India operations, and other satellite zones in the area such as El Realito and Tarachi.
Geology
The La India mine lies within an extensive ancient volcanic field. It is in an area dominated by outcrops of andesitic, dacitic and felsic volcanic tuffs from different explosive volcanic events that were affected by large-scale north-northwest-striking faults and intruded by granodiorite and diorite stocks. Canyons cut through the uppermost layers to expose the Lower Series volcanic strata.
Mineralization
La India lies in a large area of intrusion-related alteration dominated by volcanic-hosted high-sulphidation epithermal-hydrothermal gold, silver and porphyry-related gold deposits. Such deposits may be present as veins and/or disseminated deposits and/or breccias. The La India mine deposit area is one of several high sulphidation epithermal mineralization centres recognized in the region.
Epithermal high-sulphidation mineralization at the La India mine developed as a cluster of gold zones (Main, La India, El Cochi and North zones) aligned north-south, and El Realito aligned northeast, within a spatially related zone of hydrothermal alteration in excess of 20 sq. km in area. Gold mineralization is confined within zones of argillitic alteration originally containing sulphides, and subsequently oxidized.
Mineralization at Chipriona consists of what appears to be structurally controlled gold- and silver-rich veins, stringers and breccias with significant zinc, lead and copper content in sulphides.
The El Realito mineralization is found in northeast-striking subvertical parallel structural corridors of breccia that appear to have acted as conduits, bringing gold and silver mineralization into the favourable subhorizonal volcanic rock layers (the lower porphyritic dacite). El Realito remains open along strike (northeast and southwest) and shows significant potential at depth.
Surface outcrop mapping and drill-hole data so far indicate that the gold system at the Tarachi deposit is likely best classified as a gold porphyry deposit.
Mining
The La India mine is a collection of deposits grouped into three open pits – North, La India (Central) and Main – that provide ore for a heap leach pad located just west of the North pit. Operations use traditional open pit mining techniques with bench heights of 6 metres and utilize front-end loaders, trucks, track drills and various support equipment. The potential development of satellite deposits provides an opportunity to extend mine life.
In 2022, ore production will transition from the Main Zone pit, which is expected to be depleted in the first half of the year, to the La India pit and the El Realito pit.
Processing
La India’s processing flow includes a three-stage crushing process followed by a heap leach operation. Cyanide leach solution percolates through the heap to the lined solution-collection ditch that routes it to a double-lined pregnant collection pond. A zero-discharge water balance is maintained at the heap leach facilities. The gold adsorption, desorption and refining facility (ADR plant) consists of two parallel trains of six 3.5-tonne carbon adsorption columns and a Zadra strip with electrowinning. Gold-silver doré bars are produced in the refinery. The plant is designed to process leach flows from up to 6.0 million dry tonnes of ore per year (16,438 tonnes/day). Ultimate gold recovery is estimated at 69% when leaching is completed.
Exploration
Due to the success in conversion and step-out drilling at Chipriona in 2021, the Company reported a significant increase in indicated mineral resources at year-end 2021 and confirmed the high-grade silver values that typify the Chipriona sulphide deposit in contrast to the traditional low-grade oxide ore of the La India heap-leach operations.
Mineralization at Chipriona consists of structurally controlled gold- and silver-rich veins, stringers, disseminations, stockwork and breccias with significant zinc and lead content in sulphides. Surface mapping and sampling have traced these stacked, sub-parallel structures within the Chipriona mineralized corridor, which ranges from tens of metres to a few hundred metres in width over a northwest strike length of at least 3,200 metres, of which 2,300 metres has been confirmed through drill-testing. Mineralization has been intersected in the corridor from surface to a depth of approximately 275 metres. Currently, the mineralization is open towards the southeast and down dip, while other poorly exposed mineralized structures remain untested.
The significant polymetallic mineralization intersected near surface at Chipriona over substantial widths suggests the potential for bulk mining of lower-grade mineralization in stockwork zones that surround high-grade feeder zones.
Another target on the property is Tarachi, which is a large low-grade gold porphyry deposit with satellite epithermal mineral occurrences discovered in 2010. The gold system at Tarachi is best classified as a wallrock gold porphyry deposit, comprising sheeted veins that deposited gold within the wallrock outside the source dacite porphyry intrusions, suggesting that it has the potential to grow into a much larger deposit.
The Company believes the growing mineral resources at the gold- and silver-rich Chipriona sulphide deposit warrant continued exploration for sulphide-type mineralization in the extensions of the Chipriona structural corridor and other mineral occurrences in the vicinity of La India mine, including sulphide mineralization below leachable ore in the existing open pits.
At the La India mine in 2022, the Company expects to spend approximately $2.6 million for 13,000 metres of drilling to investigate for the extensions of oxide targets near the Main Zone and to grow and infill the Chipriona polymetallic sulphide deposit.
Development Projects
The La India heap leach pad construction phase III (occupying the now exhausted North Zone pit) was completed in the fourth quarter of 2021. The heap leach pad phase III provides sufficient capacity to stack the remaining ore in mineral reserves.
El Realito haulage road construction was completed in the fourth quarter of 2021. Pre-stripping of the El Realito pit is underway and is expected to be completed early in the third quarter of 2022.
In 2022, the Company will continue to conduct metallurgical test work to assess the viability of building facilities to process sulphide and polymetallic ore style of mineralization that are present on the property.
The Company is currently evaluating the potential to mill the Chipriona and La India sulphides to produce a flotation concentrate yielding an average of approximately 75,000 ounces of gold equivalent per year. Given its location, the project would benefit from the existing La India infrastructure which would reduce capital expenditures.