Magdalena is an old gold and silver district that is currently the mining centre for five active mines and developments. The Santa Gertrudis property was the site of historic heap-leach operations that produced approximately 565,000 ounces of gold between 1991 and 2000. Substantial surface infrastructure is already in place on the property including pre-stripped pits, haul roads, water sources and buildings.
The exploration program at Santa Gertrudis in 2021 totaled 53,000 metres in 115 holes, with work focused on expanding the oxide mineral resources, testing new targets and continuing metallurgical studies. An infill drilling program to convert the oxide mineral resources into mineral reserves in the Cristina and Central Trends was also initiated during the year.
As at December 31, 2021, open-pit indicated mineral resources were estimated at 4.8 million tonnes grading 0.64 g/t gold (99,000 contained ounces of gold) and 4.8 g/t silver (739,000 ounces of silver) with inferred mineral resources estimated at 23.5 million tonnes grading 1.14 g/t gold (858,000 contained ounces of gold) and 2.1 g/t silver (1.6 million ounces of silver), while underground inferred mineral resources totalled 7.3 million tonnes grading 3.5 g/t gold (821,000 contained ounces of gold) and 18.3 g/t silver (4.3 million ounces of silver).
Exploration drilling in 2021 at the Amelia deposit resulted in improved geological and structural modelling that has allowed for the projection of high-grade structures at depth approximately 120 metres below the mineral resources defined at year-end 2021.
Amelia is one of three deposits that comprise the Trinidad Trend and is the site of a previously operating open-pit gold mine. High-grade gold mineralization can be found in multiple parallel structures that commonly correspond to lithological contacts. The Amelia deposit strikes east-west for a length of approximately 900 metres and dips steeply to the north. Most of the open pit (oxide) material lies between surface and 140 metres depth, while the underground mineral resource below the open-pit mineral resource has been extended to a depth of approximately 700 metres.
As of December 31, 2020, the underground inferred mineral resource at Amelia totalled 785,300 ounces of gold and 6.2 million ounces of silver in sulphide (6.4 million tonnes grading 3.84 g/t gold and 30.8 g/t silver) and 93,700 ounces of gold and 220,000 ounces of silver in oxide (1.6 million tonnes grading 1.8 g/t gold and 4.3 g/t silver). The year-end 2021 mineral resources at Amelia are included in the overall mineral resource estimate at Santa Gertrudis.
The Espiritu Santo zone, discovered in 2019 at a location 500 metres east-southeast of Amelia, includes high-grade gold and silver mineralized structures at shallow depth.
The Santa Teresa zone contains a small historical pit located 3.2 km southwest of the Amelia deposit. During 2020, Agnico Eagle's drilling campaign at Santa Teresa discovered shallow high-grade oxide mineralization that remains open in all directions. As of December 31, 2021, the Santa Teresa oxide deposit was estimated to have an initial inferred mineral resource of 2.0 million tonnes grading 1.04 g/t gold (65,900 ounces of gold), which is included in the open-pit mineral resources at Santa Gertrudis.
The Company is currently evaluating a potential production scenario at Santa Gertrudis that utilizes a heap leach for lower-grade mineralization and a small mill facility to process higher-grade ore. The Company believes that the Santa Gertrudis project has the potential to be a similar size operation to La India.
Geology
Northern Sonora has three northwest-trending mineralization corridors, which each have distinctive regional geological features. Santa Gertrudis covers a potential strike length of 25 km of the favourable Cretaceous-age intra-caldera sedimentary belt.
Mineralization
Three corridors with favourable geological formations have been identified on the property, with a potential strike length of 18 km. Within the corridors there are nine mineralized zones with multiple deposits; the mineralized deposits form trends that are hosted mainly by units within the sedimentary Morita, Mural and Cintura formations. Limited drilling has been completed between the deposits.
There appear to be three types of gold-silver mineralization (oxide, transitional and sulphide) at Santa Gertrudis. There is stratabound replacement mineralization in calcareous siltstone or on the margins of limestone. In addition, the Company's prospecting has identified high-grade mineralization along northeast-striking fractures that crosscut the stratigraphy and that appear to be important mineralization conduits.
Exploration
Project development and exploration costs for Santa Gertrudis in 2022 are estimated at approximately $19.0 million. Regional exploration includes $13.2 million for approximately 35,500 metres of drilling focused on expanding the mineral resources and testing extensions of high-grade structures such as the Amelia deposit and exploring new targets, and $3.5 million for approximately 16,500 metres of drilling will primarily be for infilling open pit deposits. Another $2.3 million are expected to be spent on internal studies and metallurgical work.