Summary:
The Project area is prospective for several deposit types. The Hod Maden properties are located in the Eastern Pontides metallogenic province, a tectonic belt comprising part of a volcanic island-arc system. The current view on the genetic model for Hod Maden favors a sub-volcanic hydrothermal model with the bulk of the breccia style mineralization formed between the epithermal and porphyry levels.
The Hod Maden deposit is developed within a NNE-SSW trending subvertical structural corridor (Hod structural corridor) extending up to 1 km and characterised by intense hydrothermal alteration. The mineralisation comprises a paragenetically complex assemblage of Au-Ag bearing polymetallic quartz-sulphide veins, with local associated stratabound replacement type semi-massive to massive sulphide mineralization (Callan, 2013).
The geology of the area comprises Jurassic to Upper Cretaceous sedimentary, dacitic-andesitic brecciated volcanics and volcano-sedimentary lithologies. For the deposit seven main geological units have been identified:
- Overburden;
- Dacite Breccia;
- Andesite Breccia;
- Chlorite Andesite Breccia;
- Volcano-sedimentary;
- Gypsum Volcano-sedimentary;
- Massive Pyrite/Massive Pyrite - Enriched.
The mineralisation is predominantly hosted within the chlorite andesite breccia and the massive pyrite/enrichment zone. The hangingwall and footwall are represented by the dacite breccia and gypsum volcano-sedimentary units, respectively.
Significant mineralization identified on the property occurs within the Hod Maden Fault Zone, which at surface is a broadly north-northeast striking corridor of gossanous and locally argillic/phyllic hydrothermal alteration, up to 300 m wide, that extends for more than seven kilometres. Locally, it has intense pyrite/chalcopyrite mineralization with a significant component of supergene clay alteration.
The deposit is partitioned into a northern Main Zone and the contiguous South Zone, with the third area of mineralization located 500 m further south at the old Russian Mining area.
Main Zone: At least two styles of high-grade gold-copper mineralisation have been identified at the Main Zone:
1. The predominant multiphase quartz-sulfide (pyrite-chalcopyrite) ± hematite/jasper breccia bodies; and
2. Semi-massive to massive sulphides (pyrite-chalcopyrite).
Prior to 1923, small-scale mining by Russian mining interests of narrow, high grade polymetallic veins was undertaken in the now-named old Russian Mining area. Ancient slags have also been intersected in alluvial material overlying the Main Zone. The two primary mineralisation styles are related to different mineralising events, with the semi- to massive sulphide mineralisation representing an earlier mineralisation event and the multiphase breccia a later epigenetic (perhaps deep epithermal?) event. The Main Zone deposit is subvertical in nature, and currently has dimensions of around 400 m in length (N-S), 50 - 70 m true thickness, and a down-dip extension in excess of 300 m.
Overall, the highest grade gold-copper mineralisation at Hod Maden (typically >15 g/t Au but locally >100 g/t Au, and 2+% Cu) is aligned along the eastern margin of the Main Zone: this domain of very high grade mineralisation is typically 15+ m thick (true width), is remarkably continuous in both the vertical and from section to section, and currently contains a substantial majority of the in-situ metal content of the Hod Maden deposit. All mineralisation intersected to date at Hod Maden Main Zone is sulphide; no oxide (and only limited supergene enrichment occurs near surface - minor replacement of chalcopyrite by chalcocite), which is interpreted to be a direct result of the high erosion rates experienced in rugged terrains.
Hydrothermal alteration associated with the gold-copper mineralisation at Main Zone is dominated by chlorite, with the flanking wall rocks typically displaying argillic and phyllic alteration assemblages. At vertical depths of 450 m or more below surface, late-stage anhydrite brecciation of the multiphase gold-copper breccias is common and results in the dilution of pre-existing gold-copper grades. Both the form and source of this anhydrite is unclear, with the main possibilities being that it represents a “cap” to a deep, yet undiscovered intrusive phase, or may simply be to fluids circulating within the Hod Maden Fault Zone. Deep drilling will be required to better understand the nature and distribution of this anhydrite.
From a geochemical perspective, the Hod Maden gold-copper mineralisation contains only minor concentrations of Ag and trace concentrations of deleterious elements such as As, Sb, Bi, and Hg. These characteristics will play an important role in future development studies, as metallurgical studies completed to date have shown the amenability of Hod Maden ores to produce high quality flotation concentrates.
The South Zone is hosted dominantly in dacitic volcanic rocks and breccias, and comprises network quartz veins, veinlets, and breccia. Pyrite is the dominant sulphide phase, with relatively minor chalcopyrite. In contrast to the Main Zone, where chlorite is the dominant alteration mineral phase associated with gold-copper mineralisation, sericite dominates in the South Zone. Both hematite and jasper also occur but in significantly lower abundances within the South Zone. Exploration drilling will continue to evaluate the resource potential in the South Zone and will progressively move southwards towards the area of the pre-1923 Russian mining activity.