Summary:
The Hawiah volcanogenic massive sulphide (VMS) deposit is located on the eastern limb of a regional scale antiform in the Group 2 mafic volcanics of the Wadi Bidah Mineral Belt (WBMB).
VMS deposits form at or slightly under the sea floor by the exhalation of metal rich plumes and subsequent settling on or replacement of the fine grained sediments. They are tabular in nature and characterised by strong geological continuity over 100s of metres to several km in their undisturbed form.
The Hawiah deposit forms a prominent north-south trending ridgeline exposed over a total length of approximately 4,500 m, with a thickness that typically varies from 1 m to 15 m. The pronounced ridgeline is due to the formation of a siliceous gossan representing the oxidised, near surface portion of the original VMS mineralised horizon. The rock package comprises a suite of gossanous ex-massive sulphides, chert breccias, banded iron stones and intermediate volcanic breccias. The deposit has been subject to varying degrees of supergene alteration as a result of groundwater interactions.
The deposit comprises four oxidation domains; oxide, oxide-transition, transition and fresh. The oxide and oxide-transition domain typically shows supergene gold enrichment and copper and zinc leaching, while copper enrichment from supergene processes is evident in certain parts of the transitional domain. The fresh mineralised domain is dominantly pyritic stratiform massive sulphide containing fine grained copper sulphides (chalcopyrite) and zinc sulphide (sphalerite) and is characterised by low base and precious metal grade variability.
Dimensions
Mineralisation modelled comprises a continuous subvertical tabular layer for approximately 4.5 km along north to south strike at outcrop. Localised minor pinch outs occur, which are not significant. Two major zones (lodes) of down-dip extent have been defined (the Camp Lode in the south and the Crossroads Lode in the north) which plunge approximately 25°to the south for 1.5 km (Camp) and 1.7 km (Crossroads) to approximately 660 m below surface at Camp and 830 m at Crossroads in the north. The mineralised layer normally has a thickness of between 1 m and 15 m and thins towards the edges of the lodes. The central portions of the deposit between the main lodes extends vertically to between 100 m and 200 m.
The mineralised zone bifurcates in some portions of the deposit and this is clearly seen in gossan mapping and drilling in localised areas of the Central Lode and Camp Lode in the southern part of the deposit.
Al Godeyer deposit
The Al Godeyer VMS deposit is located on the western limb of a regional-scale antiform within the locally known, ‘Group 3’ volcanoclastic and epiclastic units of the Wadi Bidah Mineral Belt. The Al Godeyer deposit is expressed at surface by a northwest-southeast trending gossan that forms a slight ridgeline exposed over a length of approximately 1,250m, with a thickness that typically varies from 2m to 13m. The gossan outcrop strikes approximately west to east for a further 300m in the southern area, and a fault has been interpreted to explain the sudden strike change. Away from this main deposit area, the gossan horizon can be traced discontinuously along strike for an additional 800m.
The deposit comprises three weathering/alteration domains; Oxide, Transitional, and Fresh, within which different resulting facies are described. The oxide and transition domains typically show supergene gold enrichment and copper depletion. The fresh mineralised domain appears to be a dominantly pyritic stratiform semi-massive to massive sulphide body.
The Oxide domain mineralisation at the Al Godeyer is a combination of gossan, saccharoidal silica and haematitic cherts derived from leaching of the semi-massive to massive sulphide deposit. Higher-grade gold mineralisation is typically associated with saccharoidal silica facies, similar to the Hawiah deposit.
In the Transition domain, mineralisation is typically characterised by its dark grey to black colour due to patrial oxidation of the semi-massive to massive sulphide. The base of the transition zone is predominantly defined by the observed sulphide state, where dark grey altered sulphides become yellow un-oxidised massive pyrite at depth. Transition material is analogous to that of the Hawiah deposit albeit without a noticeable enrichment in copper.
The central portion of the deposit is the thickest and contains mineralisation elevated in gold, copper, zinc and silver, which extends 300m to 400m along strike and extends to at least 200m below surface. The northwest and southeast areas have not been tested below the oxide and transition domains.