Regionally the Marudi Property is underlain by Proterozoic metasediments of the Kwitaro Group and the younger Southern Guyana Granite Complex. The Kwitaro Group is mostly comprised of shallow water metasediments with interbedded basic volcanic strata that are metamorphosed to amphibolites facies. The Southern Guyana Granite Complex is part of the tectono-thermal Trans-Amazonian Orogenic Cycle which resulted in block faulting, crustal shortening, folding, metamorphism, and anatexis.
The Kwitaro Group in southern Guyana occurs as five discrete metasedimentary blocks, each several hundred square kilometers in extent that are bounded by granites of the Southern Guyana Granite Complex. The Kwitaro Group is age dated at 2,090 Ma. +/- 42 m.y. The Marudi Formation at the base of the Kwitaro Group consists of metachert and interbedded pelite, quartz pebble conglomerate, and amphibolites (probably a basalt or andesitic protolith. The pelites show graded and current stratification, and the quartzites display wide-spaced fracture cleavage. Dips of planar structures and mineral lineation vary from horizontal to steeply dipping to vertical. Mesoscopic shear folding is tight to open.
Marudi geology is dominated by the Marudi Formation that includes a lower pelitic unit, a medial metachert (“quartzite”), and a meta-andesite unit with subordinate tuff and ironstone. These rocks are overlain by a massive unit of orthoamphibolite (metabasalt). Metasedimentary and metavolcanic rocks have been subjected to upper greenschist and lower amphibolite grade regional metamorphism.
A review of core at Mazoa Hill has provided the most complete and detailed descriptions of the “quartzite” unit which hosts important gold mineralization discovered at the Marudi Property. The major rock units from footwall to hanging wall include meta-andesite, metachert (“quartzite”), and muscovite schist with chert silicate magnetite iron interbeds. The medial “quartzite” horizon consists of three rock units, a basal meta–andesite with tuff, middle magnetite-bearing metachert, and upper silicate – oxide ironstone and metachert.
Meta-andesite - The meta-andesite is a dark green, compact, massive rock with no internal fabric and largely composed of amphibolite and feldspar. Altered pyroxenes and calcite amygdules occur over specific zones. Deuteric alteration products – epidote schlieren, white calcite veinlets and scattered bits of red jasper are found throughout the unit. Very fine-grained chilled zones and incipient breccia in the upper few metres of the flow are in sharp contact with the overlying metachert.
“Quartzite” - The gold bearing metachert (“quartzite”) horizon overlying the meta-andesite is a pale blue-grey, sometimes white unit, commonly marked by white quartz stringers and veins near the contact. The most prevalent minor component is iron oxide which is pervasive as fine streaks and dusty clouds through the interlocking quartz grains. The oxide in the fresh rock is commonly magnetite. Iron sulphide occurs as pyrrhotite and pyrite and can display two habits in the quartzite. Pyrite, if present, can be sparsely disseminated and is coarser than the associated pyrrhotite. Total sulphide is commonly one to two percent. Blocks of quartzite up to 5 m in diameter indicate pervasive silica flooding. Estimated thickness of the metachert unit is approximately 40 m.
Magnetite-silicate iron formation - At Mazoa Hill the magnetite-silicate iron formation (referred to as “banded iron formation” or BIF) comprises a 0.5 m bed consisting of iron silicates and garnet. Medium green intervals of fine dense massive iron silicate (chlorite? annite?) three to 10 cms in thickness are separated by one to three cm layers of brown to beige garnet crystals. Magnetite occurs as a one to two cm compact bed that commonly defines the upper contact zone and can continue as thin layers up-section. One to two cm thick chert beds consisting of cryptocrystalline dark blue grey silica thick also occur.
Metasedimentary and metavolcanic units at the Marudi Property have been complexly deformed with at least two local and three regional generations of folding recognized. The Marudi Property is dominated by chevron style, upright early folds with northeast trends and deep penetrative fabrics on outcrop scale. Refolding along subsequent north-northwest striking cross folds has produced complex locally tight folds and parasitic folds, along or near fold axes.
Fold axes and beds have been offset by a significant northwest striking fault that cuts the Mazoa Hill anticline. Displacement on this fault is uncertain. A significant northeast trending fault is mapped between Marudi Mountain and Mazoa Hill. Displacement on this fault is unknown at present. Numerous small northeast striking faults were mapped in trenches at Mazoa. At Marudi Mountain these small faults generally strike north to north- northwest. Displacement on these faults that predominantly show reverse movement ranges from a few meters to tens of meters. Other east-west faults at Mazoa Hill and Marudi Mountain do not show significant displacement.