The important Au-Ag occurrences in Santa Cruz Province are confined to the Deseado Massif. The potential for important gold-silver mineralization was recognized in the Deseado Massif some 25 years ago. The Deseado Massif is a plateau consisting of Middle- to Upper Jurassic acid volcanic and volcaniclastic rocks that host fracture-controlled epithermal Au-Ag mineralization. Precious metal mineralization is related to LateJurassic magmatism.

The gold-silver deposits are hosted in silicic volcanic and volcano-sedimentary Jurassic rocks related to arc or back-arc settings in Andean or extra-Andean settings. The ore geology, textures, mineralogy, restricted alteration and geochemistry of these mineralized occurrences indicate that they belong to the epithermal class of precious metal deposits. The deposits are mainly associated with quartz +/- calcite +/- adularia +/- illite alteration assemblages interpreted to represent low and intermediate sulphidation epithermal type deposits.

Precious metal deposits generally occur in tectonically controlled structures with quartz fill, frequently brecciated in nature. Mineralization is generally associated with discrete banded quartz vein structures ranging in width from 0.5 to over 5 m, although a disseminated form of weak stockwork quartz veining of less than 0.5 m width intermediate to the principal quartz structures does also occur in some instances. Strong lithological control may occur. Dating in a few instances suggests that hydrothermal activity is several million years younger than peak magmatism. The presence of surface features like silica sinters, veins interpreted to be feeder structures, carbonate-lacustrine deposits and silicic lithocaps related to steam-heated waters in the water-table, indicates that the tops of some systems have been preserved. Erosion of younger sedimentary and volcanic cover is now exposing these systems and is suggesting that large regions or tectonic blocks are highly prospective for epithermal mineralized systems at depth.

The La Paloma and Martinetas epithermal systems are classic “low sulphidation” type deposits consisting mainly of quartz with adularia and free Au, minor amounts of sulphides (except at Sulfuro where a relatively high sulphide content occurs), and weak alteration haloes. Classic low sulphidation textures like lattice textures, crustiform-colloform banding, comb quartz, etc., are common. They may also be associated with anomalous amounts of arsenic (As), mercury (Hg), or antimony (Sb).

The study is based on conventional open pit mining.

The Don Nicolás mine design specifies 5-m benches and has adequate phase geometry to achieve the required productions. The design calls for annual mill throughput of 350,000 t of ore. Mining will advance simultaneously in two different pits with two to three pit phases generally active at any time. The vertical advance rate of the pits will be relatively low, with a maximum of eleven 5-m benches per phase per year.

The process plant has been designed to treat gold-bearing material at the rate of 972 t/d, equivalent to 350,000 t/a.

The crushing circuit will reduce the mined material size from a nominal top size of 500 mm to a product size P80 of 6.5 mm in preparation for the grinding process.

The grinding circuit will reduce the size of the crushed material to a final product size with a product P80 of 75 µm, suitable for the subsequent gold recovery by gravity concentration and cyanide leaching processes. The grinding process will be a single-stage operation with the ball mill in closed circuit with classifying cyclones.

The gravity concentration circuit will produce a concentrate containing coarse gold from the grinding circuit, and will treat the gravity concentrate on a shaking table to upgrade the concentrate suitable for its smelting at the refinery.

The gravity concentrate will be stored until a sufficient amount has been collected for the tabl ........