Equinox, through its indirect wholly-owned subsidiary Mineração Aurizona S.A. (MASA), owns all surface rights required for the operation of the Aurizona Mine.
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Summary:
The main deposit type in the Aurizona project area is greenstone-hosted orogenic gold, a subtype of the larger orogenic class of gold deposits.
The primary mineralization style on the Property consists of orogenic-style gold deposits, typically associated with the quartz diorite and feldspar quartz diorite units in brittle-ductile structures like the ASZ. Significant gold occurrences in the project area include the Piaba, Boa Esperança, Tatajuba and Genipapo deposits, as well as the Mestre Chico and Micote targets.
Piaba is a structurally-controlled, tabular, orogenic gold deposit with a strike length of ~3.3 km, width of 10 – 50 m, and down-dip extent of at least 700 m, beyond which the deposit is sparsely explored. The deposit is hosted in the brittle-ductile ASZ that is ENE-WSW striking and steeply north dipping to the NNW.
Within the Piaba deposit, the ASZ system is divided into ten shear zones and/or brittle faults, partially segmenting the deposit with limited offsets. The maximum offset observed is 100 m, whereas most offsets are in the order of 10 m. The Pirocaua fault zone at the east-northeast end of the deposit is a significant structure. This brittle fault zone is up to 350 m wide and locally disrupts the Piaba gold zone with a maximum offset of 75 m. At the western end of Piaba on section 1900W there is a northwest striking fault, which truncates the gold zone at depth. Near surface mineralization continues west of the fault in Piaba west area although the possible offset of the mineralization at depth has not been tested.
Mineralization is primarily hosted in the quartz diorite that is also described as a dike-like c. 2.0 Ga granophyric granodiorite (e.g. Freitas and Klein, 2013; Klein et al., 2015) but has also been interpreted as a cataclasite unit. Ore-related alteration includes strong to intense sericite carbonate-silica-sulphide alteration in the central part of the structure (i.e. in the quartz diorite) flanked by chlorite-dominant alteration in the footwall and hangingwall. Gold occurs in thin, millimetre to centimetre-scale, and quartz -carbonate ± sulphide± tourmaline bearing shear veins. Native gold is rarely observed at wall rock-vein contacts. Sub-horizontal quartz-carbonate extensional veins commonly cut shear veins and can contain gold. Increased vein density and sulphide abundance are the best indicators of gold mineralization.
The Boa Esperança deposit is located approximately one kilometre south of the Piaba deposit and consists of four sub-parallel gold-bearing zones that are continuous along strike for ~1000 m. The four gold-bearing zones are each about 5 ± 2 m wide and developed in a corridor ranging from 40 – 75 m in width, narrowing to 20 m at the northeastern end where there are generally just two zones. The four gold bearing zones coalesce within the saprolite and laterite portions of the eastern margin of the deposit. The deposit extends to at least 230 m below the surface and is hosted within a brittle-ductile structure trending ENE-WSW and dipping steeply (80°–90°) to the NNW.
Mineralization is hosted in strongly altered and deformed Aurizona Group rocks, likely derived from the adjacent Aurizona Group diorite, gabbro, and minor metasedimentary rocks. The mineralized corridor shows moderate to strong silica-sericite-albite-carbonate alteration, along with increased disseminated pyrite (2 – 5 modal percent) and density of quartz-carbonate-sulphide veins.
The Tatajuba deposit is also hosted within the ASZ, with the eastern end of the deposit located ~2 km west of the western end of the Piaba deposit. The Tatajuba deposit comprises a tabular zone that is east-west striking and steeply north-dipping; the zone measures ~700 m long, 5 – 30 m thick and 300 m in downdip extent. Within the eastern portion of the Tatajuba deposit, the ASZ system is interpreted to be cross-cut by subvertical NNW-trending structures. The maximum offset observed is between sections 200E and 300E, where the deposit is offset by 10 m, through sinistral shearing and/or faulting.
Gold mineralization is hosted in a subvertical to north dipping quartz diorite unit with concordant shear veins and moderately south dipping extensional veins. The quartz diorite shows granular cataclastic texture and is silica-carbonate-sericite-altered, grading outward into strongly chlorite-carbonate altered rocks. Shear and extension veins are mostly restricted to the tabular quartz diorite unit, with shear veins sub-concordant to this unit and consisting of quartz ± carbonate ± chlorite ± pyrite ± arsenopyrite. Extension veins appear to be moderately south dipping to sub-horizontal and consist of quartz with ~1–10% pyrite. Visible gold occurs in both vein types but is most abundant within the extension veins. Gold values are correlated with arsenic and associated with arsenopyrite.
The Genipapo North and South deposits are located about one kilometre east of the eastern margin of the Piaba deposit, with Genipapo North approximately 400 m north of Genipapo South. These deposits form in splays off the ASZ. The geology, geochemistry and magnetic data indicate a horsetail structure off the ASZ structure. Numerous fault structures and discontinuous splays of metavolcanoclastic and ultramafic units have been interpreted at Genipapo and the surrounding area. The metavolcaniclastic sequences are comprised of metatuffs, metagraywackes, phyllites and are in fault contact with ultramafic rocks. Gold mineralization is associated with shear-hosted smoky quartz veins and millimetre-scale extensional veins that form a stockwork. The mineralization forms in quartz ± albite ± sericite alteration with pyrite and arsenopyrite minerals. There is a strong correlation between gold and arsenic.
Touro is located about 20 km southwest of the Piaba deposit. The Touro deposit is hosted in a coarse-grained DRT and strongly deformed MVC rocks from Aurizona Group. A regional northeast- southwest treading mylonitic shear zone the host rocks which are cut by late andesite and aplite to pegmatite dykes.