Summary:
The deposit is best described as a brittle, thrust-dominated, competency-controlled orogenic gold low sulphide system developed post ductile deformation.
Gold occurs along the 25km strike length of the Hill End anticline (Harper, 1918; Joplin 1949; Seccombe and Hicks, 1989; Windh, 1995), including the historically important Hawkins Hill mines at Hill End, where the late Silurian Chesleigh Formation hosts gold-bearing, bedding-parallel, laminated quartz veins and associated structures on the east limb of the Hill End anticline. At Hill End, the anticlinal hinge consists of two closely spaced anticlines and an intervening syncline.
Previous mining at Hawkins Hill worked a series of rich, gold-bearing veins over a strike length of 1 km and to a depth of 200m from the surface in places.
Exploration north from Hawkins Hill to Reward and Germantown indicated that bedding-parallel veins only showed significant gold mineralization (>10 g/t) in a subvertical and N-striking mineralized corridor on the east limb of the westernmost anticline in the core of the Hill End anticline.
From 2007 to 2010, the Amalgamated adit (640 Level) was extended to intersect a new 286m shaft, known as Reward Shaft. The shaft also provides access to the Paxton’s vein set above the 640 Level. The Consolidated 695 Level (35m above Amalgamated) was widened (from 1.5m to 2.3m) and heightened (to 2.5m) from the adit to the Phillipsons Vein.
Level development and drilling in the Reward mine have intersected 14 bedding-parallel vein sets within a 360m thick sequence of metaturbidites on the steeply E dipping anticline limb. Vein names date from the 1870s; on 640 access level. The most westerly vein (Lady Belmore) is followed by a 90m thick metasandstone unit. Then, from west to east, named veins are spaced stratigraphically at 5m to 25m apart and are sequentially encountered in higher levels in the mine. The principal veins are:
• Brand and Fletcher’s;
• Amalgamated;
• Phillipson’s;
• Mica;
• Star of Peace;
• Middle;
• Paxton’s;
• Steven’s (Moustaka’s);
• Calcite (Herman’s);
• Frenchman’s (Star of Hope);
• Far East;
• Rowley’s, and;
• Mountain Maid.
In the Reward mine, metaturbidites young to the east and contain fining upward cycles. Diagenetic and syndeformational low-grade alteration (chlorite, calcite, muscovite, sericite, epidote, pyrite, and arsenopyrite) of sandstone-dominated metaturbidites is common throughout the mine sequence. However, bedding-parallel laminated quartz veins are restricted to shale beds (now represented by cleaved black slates) in either sandstone or shale dominated turbidites.
The principal bedding-parallel veins in the Reward mine have a maximum thickness of ~75 cm. In narrow slate beds they may be represented by individual veins or sets of two to four veins (e.g., Mica and Paxton’s). They initially appear to be constant features over 100s of meters; however, in detail along the strike and downdip they tend to have variable persistence, thickness, character, and grade distribution (1,000 g/t).
Mineralization
The principal gold mineralisation is associated with a series of bedding parallel quartz veins and associated saddle reefs occurring along both limbs and across the axis of the Hill End Anticline. veins are generally confined to slate units interbedded within coarser metasandstone units.
Individual veins are narrow (0.05 to 0.3m wide) strike 190° and dip ~60°E. On some sections, up to 8 mineralised veins have been recorded. Minor near-horizontal, laminated (crack-seal), "leader" veins intersect layer-parallel veins. This intersection forms nearhorizontal north plunging high-grade ore shoots. Also present are minor steeply dipping, crosscutting "spur" veins and crosscutting faults which kinematic analysis suggests resulted from minor dextral strike-slip movement. Steeply plunging high-grade ore shoots also formed at the intersection of these crosscutting structures and layerparallel veins.
Dimensions
Mineralisation occurs as a series of 14 stacked quartz vein sets that strike approximately north-south and steeply dip to the east. The defined Mineral Resource extends for 700m along strike, has a horizontal combined width of around 70m and a vertical height of about 250m. The top of the Mineral Resource occurs between 70m and 90m below the surface.