This project is under application under EPMA 26994
The Silverwood / Lucky Valley (Project) geology and structure is moderately well understood, though current knowledge of the mineral potential of the area is less well known.
The Project area has one operating mine, a marble limestone quarry at Elbow Valley operated by the Unimin Pty Ltd, a fully owned subsidiary of the international Belgian company Sibelco.
Mineralisation in the area consists of scattered historic, alluvial gold workings and some minor hard rock gold workings, there is also a number of copper and base metal shows that have been worked in the past, and a number of limestone occurrences throughout the area.
Traprock (TML) views the prospectivity of the area as very promising, with the potential to discover gold in limy marl and calcareous sediments, also within altered limestones and skarns, carbonaceous shales and intrusion related mineralisation.
There is also the possibility of discovering copper, lead, zinc and silver in volcanic hosted massive sulphide bodies and also mineralisation hosted by porphyritic intrusion related systems. All the differing styles of mineralisation are evident within the Project area, except gold in limy sediments, though there are more than a few locations within the Project, where gold has been found, in close proximity to outcropping limestones, and related calcareous sediments including limestone clast supported breccias.
The Project has extremely good infrastructure, being 15 kilometres south of the regional centre of Warwick, 24 kilometres north east of Stanthorpe and 18 kilometres west of the small town of Killarney. The two former towns have all the medium sized machinery and other workshops required to service any ongoing maintenance for the project.
The climate in the region is temperate continental with warm summers and cool winters, with most precipitation falling mainly in the spring and early summer, annual rainfall averages 700 mm.
Gold was first reported in the eastern side of the Project area in Elbow Valley area August 1851, when a small parcel of ore was sent to Rev. W.B. Clark (the father of Australian geology). A further report of alluvial gold being recovered from the Lord John’s Swamp to the west of Elbow Valley was made in 1852 (de Havelland 1987). But it was not until 1868 that payable alluvial gold, of high quality, was discovered at Lucky Valley, the adjacent Frenchmen’s gully and other gullies.
At the head of the Lucky Valley a small hill consisting of quartz leaders within metasediments was mined, a crushing of 10.8 tonnes recovered 12 ounces 9 grams of gold (de Havelland 1987).
Between 1856 and 1970 there were 32 separate gold and base metal occurrences mined and 9 limestone occurrences identified and quarried, some of the limestone is carrying copper and zinc, and a magnetite occurrence was mined in the northern part of the Project area at Tatong (Geo. Surv. Bultitude et al 2007).
Silverwood Copper Mine: this includes the Day Dawn and Wilson’s Lodes. The workings are located along the contact between the andesitic pyroclastics (Connolly Volcanics) and the sediments of the Rosenthal Creek Formation.
Grades have been estimated upto 1.72% Cu. Copper mineralisation as chalcopyrite occurs mainly in highly silceous brecciated zone 0.3-1 metre wide.
Myrtle Copper: this is a small prospect of scattered pits and small dumps, to the south of Silverwood Copper Mine, and occurs in the same stratigraphic position.
Grieves Quarry: this deposit (Grades of 0.66% Cu, 0.73% Pb, 4.92% Zn, 1.17oz Ag, GSQ) is hosted by a sequence of coarse grained andesitic tuffs, interbedded with fine to medium grained limestone, occurring above a sequence of pillow-basalt. Mineralisation occurs as disseminated and massive sulphides.
The Project area is situated within the Silverwood Group geologic unit, which rocks are situated within The New England Fold Belt of eastern Australia, the fold belt comprising of an ancient convergent margin, active in the Paleozoic until the late Mesozoic.
The Silverwood Group is a succession of arc-related basins that developed within an ancient intra-oceanic island arc, as part of a west directed subduction zone, during the mid-Cambrian through to the late Devonian (Van Noord 1999).
The whole basin succession is 9700 metres thick, and the whole succession has been thrust over the late Devonian to early Carboniferous Texas Beds, which are adjacent to the west. The Silverwood Group have been intruded to the west, southwest and south by the late Triassic Herries and Stanthorpe Granitoids, and the group is overlain in the east and north by Jurassic sediments of the Marburg Sandstone.
The Silverwood Group comprises of varied volcaniclastic sediments from conglomerates through to sandstones and mudstones, deep marine turbidites, and limestones and limy marls. The sequence was interbedded and also overlain with volcanic rocks, which were in the main tholeiitic metabasites, dolerites, meta-andesites and meta-dacites (Van Noord 1999).
Exploration Philosophical Models and Prospective Targets.
Several differing styles of mineralisation are possibly present in the Silverwood Geological Group,
The potential to find gold in calcareous or carbonate sedimentary rocks is a good possibility, with widespread limestones and limy rocks occurrences in the Project area. These rocks are controlled within structural domains, which lithologies have been displaced by thrust faults and strike slip faulting. The limy sediments are interbedded with volcanic extrusive flows and have also been intruded by hypabyssal shallow andesitic Permian intrusives and deeper emplaced Triassic porphyritic granite.
Gold has been mined from alluvial deposits in close proximity to limy rocks and marbles, in several locations within the Project. Namely at Lucky Valley, Frenchman’s Gully and west of there, at Limekiln Gully a tributary of Lord John’s Swamp and further alluvial gold was mined at Limestone Gully all within the Elbow Valley area. There is further alluvial gold mined near Silverwood, Elbow Gully and Mendip, again in close proximity to calcareous rocks.
The possibility of finding skarn and altered limestone hosted gold, has not been tested, since most world occurrences of this style of mineralisation e.g. Carlin style, have superfine sub-microscopic gold associated with them, the gold is not readily visible, certainly by pre-1960 explorers and miners. Mapping out and assay testing of the calcareous outcrops would go a long way to testing the model.
Occurrences of intrusion related skarns and limy sediments have been mined at the Tatong Magnetite/ FeO Limestone deposit, also has been drilled at Grieves Quarry with mineralisation still untested laterally and beyond 130 metres depth. Further precious and base metal rich skarn mineralisation will come to light as past exploration has been very patchy and limited in the Project area.
There is also the opportunity to locate suitable limestone/ marble occurrences for production of lime products, as Brisbane/ Gold Coast has a potential short supply position in the short to medium term future.
Intrusion related gold and base metals, plus mesothermal quartz vein and stockworks are documented in Queensland Geological Reports of the Project area, very little drilling has been conducted in the region for precious and base metals.
The southern portion of the Project area, encompasses most of the Silverwood Group succession contact with the Stanthorpe Granite. The granite is an early Triassic even grained granite, in part porphyritic, and is predominantly a leucogranite. There are three prospects within close proximity to the contact zone, the Oaklands Copper and the Baguette Gold Working, and the Elbow Gully Alluvial Gold Working which is in situ on a faulted contact between metabasites and calcareous mudstone distally close to the Stanthorpe Granite contact.
Conclusions and Reccommendations
The Silverwood/ Lucky Valley EPMA fits into the Traprock project portfolio very well, since it is in the same region as the Herries Range and Warroo Projects and has the advantage of those efficiencies relating to lowering of costs and geological experience and expertise in similar environments.
Traprock intends to finalise data research and prospect inspection, before focussing on stream sediment and rock chip geochemical sampling on selected areas, with the aim of drilling prospective targets developed from the ground work within 18 months from granting.
To reiterate, Traprock considers the Silverwood Group geology to be very prospective for gold in calcareous sediments, also within intrusion related rocks and potential for precious and/or base metal hosted by volcanic massive sulphides style of deposits.