14 kilo Gold in Quartz Huge Specimen - Rockley Rocks eBay скачать в хорошем качестве

14 kilo Gold in Quartz Huge Specimen - Rockley Rocks eBay

Specimen Overview • Description: A single, irregularly shaped ore fragment exhibiting a brecciated and vuggy texture, with prominent white to translucent quartz veins and crystals infilling fractures within a reddish-brown iron oxide matrix. The specimen displays botryoidal and mammillary forms on oxide surfaces, indicative of secondary enrichment processes. Visible gold is not apparent without magnification, consistent with refractory orogenic gold ores where precious metal occurs as sub-micron inclusions. •Specimen Overview • Description: A single, irregularly shaped ore fragment exhibiting a brecciated and vuggy texture, with prominent white to translucent quartz veins and crystals infilling fractures within a reddish-brown iron oxide matrix. The specimen displays botryoidal and mammillary forms on oxide surfaces, indicative of secondary enrichment processes. Visible under magnification, consistent with refractory orogenic gold ores where precious metal occurs as sub-micron inclusions. • Dimensions and Morphology: Approximate dimensions not specified; appears as a hand-sample chunk with rough, oxidized exterior and internal vugs up to several centimeters across. • Mass: 14 kg • Collection Context: Sourced from an active or historical gold mine within the Lachlan Orogen, southeastern Australia. Exact mine undisclosed, but characteristics align with deposits in the western sub-province such as Bendigo-Ballarat or Stawell zones. Geological Setting The Lachlan Orogen is a major Paleozoic fold-thrust belt in southeastern Australia, spanning Victoria and New South Wales. It formed during the Ordovician to Devonian as a convergent margin system involving subduction, accretion, and collision along the proto-Pacific margin of Gondwana. The orogen is divided into western, central, and eastern zones, with the western Lachlan being the primary host for world-class orogenic gold deposits. • Host Rock Lithology: Predominantly Ordovician turbiditic sequences of the Lachlan Supergroup, including interbedded sandstones, siltstones, and mudstones such as the Castlemaine Group. These metasediments are pervasively altered and deformed, with low-grade greenschist to sub-greenschist metamorphism at 200–350°C. • Structural Controls: Mineralization is hosted in reverse-fault and fold-related quartz veins within anticlinal saddle reefs or en-echelon vein arrays. The specimen’s brecciated texture suggests formation along dilational jogs in transpressional shear zones, where seismic pumping facilitated fluid ingress. • Tectonic Evolution: Gold emplacement occurred during late-orogenic uplift phases, post-dating peak metamorphism. Key events include the Benambran Orogeny around 445 million years ago for early mineralization and the Tabberabberan Orogeny around 380–370 million years ago for later events. Mineralogy and Petrography Based on visual inspection of the provided high-resolution images: • Primary Gangue Mineral: Quartz (SiO₂) – dominant, forming milky-white to clear veins and euhedral crystals up to 1–2 cm. Exhibits undulatory extinction and minor deformation twins, indicating syn-tectonic precipitation. • Oxide Matrix: Iron oxides such as goethite and limonite – reddish-brown staining and botryoidal coatings, representing supergene enrichment. Gossan-like appearance suggests exposure to near-surface weathering. • Alteration Minerals:  • Carbonates such as ankerite or ferroan dolomite – inferred from creamy-white infills in vugs; common in orogenic systems, comprising 5–15% of vein assemblages.  • Sericite – possible in matrix, contributing to the speckled texture.  • Minor clays or chlorite – greenish tinges in matrix. • Sulfides: Not prominently visible, but typical for Lachlan ores include arsenopyrite and pyrite as less than 3–5% disseminated grains or veinlets. These host invisible gold as lattice-bound inclusions. • Ore Mineral: Native gold – likely present at 5–30 g/t grades, refractory and associated with sulfides. Visible under magnification within oxide or quartz zones. • Accessory Phases: Potential traces of tourmaline, scheelite, or stibnite in intrusion-related variants; no clear evidence in images. The specimen represents a classic ribbon or saddle-reef vein sample, with quartz-carbonate-sulfide paragenesis diagnostic of mesothermal orogenic gold. Geochemistry • Bulk Composition (Inferred): High SiO₂ over 70%, Fe₂O₃ 10–20% from oxides, minor As, Sb, W, and Te as pathfinders. Gold-to-silver ratio approximately 10:1, with low base metals. • Isotopic Signatures: Pb isotopes reflect mixed crustal-mantle sources; ⁴⁰Ar/³⁹Ar dating constrains mineralization to around 445 Ma (Benambran) or around 400 Ma (post-Tabberabberan). Low ³He/⁴He ratios (0.2–0.3 Ra) confirm dominantly crustal fluid derivation. • Weathering Profile: Supergene enrichment via Fe³⁺ remobilization has likely concentrated Au in the oxide cap, explaining the specimen’s gossanous exterior....CONTINUES IN EBAY DESCRIPTION