Summary:
Deposit Types
The interpretation of the deposit type at Toroparu is uncertain, with possibilities including an unusually copper rich orogenic gold deposit on the basis of the host greenschist metamorphic rocks and a strong control of mineralization due to competency contrasts, as well as a metamorphosed porphyry gold-copper deposit. Recent structural interpretation work suggests that Toroparu is not a classic lode type orogenic gold deposit and is unlikely to be a deformed porphyry deposit (Pratt and Smeraglia, 2022). A disseminated or sheeted vein type deposit can be used as a guide for exploration planning purposes.
Property Geology
Thin, discontinuous mineralized shear zones at the Toroparu deposit are developed mainly in the volcanic rocks. Higher grade, discontinuous shear zone hosted mineralization is narrow and mostly parallel to the schistosity. The main controls on mineralization are the west-northwest striking axial planar schistosity and vein swarms that are well developed in the volcanic rocks, and the folded contact between an intrusive complex and the volcanic rocks, particularly the contact of an igneous breccia that forms an important rheological contrast, similar to many other orogenic gold deposits that are strongly controlled by competency contrasts. The deposit dips roughly 55° to the west.
The Sona Hill deposit has similar controls on mineralization but strikes to the north and dips around 30° to the west.
Two dyke phases are present including hornblende porphyritic andesite dykes and dolerite dykes. Most dykes have an apparent thickness of less than 0.5 m, but some dykes up to 2.5 m thick also occur. The hornblende porphyrite andesite dykes are weakly to intensely deformed with schistosity roughly parallel to that of the host rock. In places, these dykes are folded. Despite being sheared and folded, the dykes are mostly non-mineralized, although some mineralized veins occur along the contacts. Some of these dykes are cut by mineralized shear zones. The dolerite dykes are fine grained, non-sheared, and non-mineralized. They crosscut gold mineralized veins, silicified zones, and shear zones. They postdate both the deformation and the gold mineralizing events.
A thick, gradational, 10 m to 35 m thick layer of saprolite with preserved mineralized quartz veins and veinlets, showing evidence of some gold leaching, is present at the surface at Toroparu and reaches up to 60 m thick at Sona Hill. A weathering profile comprised of overburden, saprolite, and a transition zone has been interpreted for the mineral resource estimate. The overburden has abundant low grade gold mineralization but little high grade.
Mineralization and Alteration
Mineralization at the Toroparu deposit estimated as mineral resources in the main zone has a footprint of around 1.3 km along strike, around 500 m across strike, and a depth of 550 m. There is a zone of mineral resources approximately 1.1 km to the southeast of the main zone with a footprint of around 400 m along strike, 230 m across strike, and a depth of 250 m. There are a few other small zones of mineral resources on the order of 100 m long along strike of and parallel to the main zone. The mineralized shear zones are narrow and discontinuous. Sona Hill has a footprint of around 950 m along strike, up to 300 m wide, and a depth of around 200 m. Sona Hill is characterized by a lower copper content. Both deposits are open at depth.
The main body of mineralization at Toroparu is characterized by three different vein assemblages.
•Gold mineralized quartz and chalcopyrite or bornite veinlets occur both in the volcanic and intrusive rocks and appear to be focused on the boundary between them, particularly within a marginal igneous breccia. Chalcopyrite and quartz are commonly coarse and intergrown. The veinlets are more abundant and thinner in the volcanic rocks, are parallel to the schistosity, and tend to have lower gold grades. The veins are less continuous in the intrusive rocks and igneous breccia but tend to be of higher gold grade and contain molybdenite. Within the intrusive rocks, the veins show an intense chlorite alteration halo. Vein swarms in the volcanic rocks are in zones up to tens of metres thick with low to medium gold grades, with scattered high grades coinciding with high chalcopyrite content. In places, the veins are folded and boudinaged, with chalcopyrite often concentrated in the boudin necks. Veins range between less than 1 mm up to a few centimetres thick. There are rare 0.4 m to 0.5 m thick veins.
• Gold mineralized chalcopyrite only veinlets occur in the volcanic and intrusive rocks. These veinlets are up to a few millimetres thick and are strongly transposed and dismembered parallel to schistosity and are also folded. In places, chalcopyrite veinlets form a scattered network in quartz veins.
• Gold mineralized quartz and molybdenite veins are also present, mostly in the igneous breccia along the intrusive-volcanic contact. These veins are scattered and contain high gold grades.
Local gold mineralized silica alteration occurs as discrete patches or as zones up to tens of metres thick that affect volcanics, intrusives, and igneous breccias. In places the silica is associated with epidote. Silica alteration is characterized by disseminated chalcopyrite and is crosscut by quartz chalcopyrite veins and chalcopyrite veinlets. In contrast with the schistose rocks, the veinlets have an apparent random orientation. Silica alteration halos occur around the chalcopyrite veinlets and have higher gold grades.