RE: Patience is the key11 Aug 2025 22:56
From GROK..
Yes, alteration and bleaching in core samples can be associated with gold and copper mineralization. These features often indicate hydrothermal activity or fluid-rock interactions that can deposit or concentrate metals like gold and copper. Here’s a concise explanation:
Why Alteration and Bleaching Are Linked to Gold and Copper:
Hydrothermal Systems: Alteration (e.g., clay, sericite, chlorite) and bleaching (color loss due to mineral leaching) are common in hydrothermal systems where gold and copper are deposited. Fluids carrying these metals alter surrounding rocks, leaving diagnostic mineral assemblages.
Mineralization Indicators:
Gold: Often associated with sericitic, silicic, or argillic alteration in epithermal or porphyry systems. Bleaching may occur due to fluid interactions removing iron oxides.
Copper: Found in porphyry, skarn, or volcanic-hosted deposits with alteration minerals like chlorite, epidote, or clay. Bleaching can signal reducing conditions favorable for copper sulfides (e.g., chalcopyrite).
Examples from Exploration:
Red Setter Gold Dome Project (Wishbone Gold PLC): Drill core showed chalcopyrite (a copper mineral) and bleaching, indicating a potential gold-copper system.
G2 Goldfields (Ghanie): Bleaching and sericite alteration with pyrite in drill core were linked to gold mineralization in shear zones.
Porphyry Systems: Bleaching and clay alteration often surround copper-gold porphyry deposits, as seen in many global deposits.
How Gold and Copper Occur in Altered/Bleached Core:
Direct Mineralization: Gold may occur as native gold or in sulfides (e.g., pyrite, arsenopyrite), while copper appears as chalcopyrite, bornite, or chalcocite within altered zones.
Proximity to Ore: Bleaching and alteration often form halos around mineralized zones, acting as a guide to gold-copper deposits.
Fluid Pathways: Bleached zones indicate fluid movement, which can transport and deposit metals along faults or fractures.
Practical Considerations:
Assaying Needed: While alteration and bleaching suggest potential, core samples must be assayed (e.g., via fire assay for gold or ICP-MS for copper) to confirm metal content.
Alteration Types: Look for potassic (K-feldspar, biotite), sericitic (sericite, quartz), or argillic (clays) alteration, as these are commonly associated with gold-copper deposits.
Exploration Tools: Hyperspectral imaging, XRF, or LIBS can map alteration minerals and detect trace gold or copper in core samples.
Conclusion:
Alteration and bleaching in core samples can absolutely contain gold and copper, as these features often signal hydrothermal systems conducive to such mineralization. However, their presence alone doesn’t guarantee economic deposits—detailed analysis and assays are critical to confirm metal grades.
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