Summary:
Campo Morado hosts volcanogenic massive sulphide or “VMS” type mineralization.
The Campo Morado district is home to several distinct deposits occurring mainly in the Campo Morado felsic volcanic unit near its upper contact. Most of these deposits occur in a roughly four kilometre long, southwest-northeast trending grouping within the central part of the Campo Morado mining concessions and are locally offset tens to hundreds of metres from one another by late extensional faults. To the northeast, the overturned Reforma and El Rey deposits are separated from the Naranjo and El Largo deposits by a major thrust fault along the axial zone of a recumbent anticline. To the southwest of these latter two deposits, the La Lucha, San Rafael and G9 deposits occur as metre scale auriferous massive sulphide lenses with associated small stringer zones at the same stratigraphic level as the Naranjo deposit. Several other massive sulphide and stringer zones occur elsewhere along a 25 kilometre long belt that extends northnortheast and south-southwest from the central district. These include La Suriana district deposits, found in a faulted sequence of strongly altered felsic to intermediate volcanic rocks about 1,000 metre higher in structural section and several kilometres to the south of the Campo Morado district.
The Campo Morado property hosts several precious metal-rich volcanic associated massive sulphide deposits, which occur in a sequence of felsic to intermediate flows and tuffs, and heterolithic fragmental rocks. Most are in the upper part of the felsic pile or at the contact with stratigraphically overlying, fine-grained, chemical and clastic sedimentary rocks. The five major lithostratigraphic units from oldest to youngest are the Guerrero Ridge intermediate volcanicsubvolcanic unit, the Naranjo sedimentary unit, the Campo Morado felsic volcanic unit, the La Canita volcanic unit and, the Reforma sedimentary unit. Two stages of magmatic pulses intrude all of these units except La Canita. One is associated with the Campo Morado felsic unit, the other being of Tertiary age.
Mineralization at Campo Morado mine consists of polymetallic volcanogenic massive sulphide deposits hosted within an Upper Jurassic to Lower Cretaceous sequence of felsic to intermediate flows, tuffs and fragmental volcanic rocks. There is strong continuity of the mineralization as demonstrated in the extensive diamond drilling and underground development.
Mineralization is of the volcanogenic massive sulphide (VMS) type. The massive sulphide horizons host polymetallic (base metal and precious metal) mineralization within a complex, layered sequence of felsic to intermediate volcanic rocks. The metals of interest include zinc, copper, gold, silver and lead.
The massive sulphide horizons of the Campo Morado deposits are mainly comprised of fine grained pyrite (iron sulphide) with a variety of other sulphide minerals that include, in descending order of occurrence, sphalerite, chalcopyrite, galena, tetrahedrite-tennantite, arsenopyrite, marcasite and pyrrhotite, traces of tin minerals, electrum (gold alloy containing 20 percent or more silver) and gold.
The base metal sulphides are found as discreet mineral grains, or more frequently, as infill mineralization between or within pyrite grains. Gold occurs in liberated form or as gold present as adhesions/binary structures with chalcopyrite and galena. This binary form comprises approximately one third of the gold content in the G9 deposit. The remaining gold is present as small adhesions or inclusions with pyrite or as multi-phase occurrences contained mainly in pyrite, in which form it is not amenable to flotation. Approximately half the silver content of G9 mineralization is closely associated with tetrahedrite, about 40 percent with pyrite and the balance with galena and various minor minerals.
Felsic flows at La Trinidad contain zones of brecciation, sulphide mineralization and alteration similar to that in the main Campo Morado area.