Trilogy Polymetallic Project
The Trilogy polymetallic deposit is located approximately 9km to the south of Kundip. Trilogy was discovered by Homestake Gold Australia (Homestake) in 1997, and is a substantial mineral deposit in its own right. Trilogy is hosted in Proterozoic rocks which overlay the Archean geology immediately south of Kundip, illustrating the multi-faceted prospectivity of the ACH tenement package.
Trilogy is located on 1,200 Hectares of freehold farmland owned by ACH and leased to local pastoralists, providing full autonomy with respect to future land use. The deposit benefits from a significant bank of historical testwork and studies which comprehensively demonstrates the technical merits of what is predominantly a base metal project (Cu/Zn/Pb) with significant precious metal credits. ACH has updated the historic resource estimate to be in accordance with JORC 2012 guidelines and is also progressing geophysical surveys along the Whoogarup Fault, a major region structure thought to be prospective for repetitions of Trilogy style mineralisation.
Trilogy has been interpreted as a sedimentary exhalative (SEDEX) style Au-Cu-Ag-Pb-Zn deposit hosted in Proterozoic aged graphitic siltstones. There are three parallel mineralised zones dipping broadly 40˚ to the SE, each typically 10m – 30m thick and separated by 5m – 30m of waste rock. Strike extent is over 320m, and down dip extent is over 300m. Mineralisation is hosted in two main units:
a. Breccia of banded sulphide matrix and lithic fragments; and
b. Highly siliceous sedimentary breccia in the footwall of the mineralised zones.
Two styles of economic mineralisation are evident:
a. Copper-gold only mineralisation, hosted mostly in late stage pyrite-chalcopyrite veining; and
b. Polymetallic (Au-Cu-Ag-Pb-Zn) mineralisation, which is also mineralised with the later stage Cu-Au veining.
Near surface oxide mineralogy consists of covellite and lesser chalcocite replacing chalcopyrite, and anglesite replacing galena. Sulphide zone mineralogy consists of chalcopyrite, galena and lesser anglesite, and sphalerite. Oxidation is evident to about 40m below surface with some oxidation of chalcopyrite extending below the top of fresh rock.
In addition to Trilogy, in 1998 Homestake discovered the Queen Sheba Prospect which is located 2km southeast of Trilogy. Mineralisation is similar to Trilogy, but pyrite rather than base metal sulphide dominated.
The Mineral Resource for the Queen Sheba deposit was last reported by Tectonic geologists in September 2011.
Data from both diamond and RC drillholes has been used in the resource calculation, with all RAB holes disregarded. The resource estimation was constrained by a lower cut-off grade of 1.0g/t Au, although some sub-grade intersections were included within the ore outline where determined appropriate.
Four geological domains were defined which primarily relate to the mineralised structures. A total resource (inferred) of 0.8 Mt @ 1.9 g/t, 3.98 g/t Ag was reported yielding approximately 50koz of gold. The structures defined remain open along strike and depth.