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Galena–Sphalerite Massive Sulphide Ore in Quartz-Carbonate Gangue - minShelf
Galena–Sphalerite Massive Sulphide Ore in Quartz-Carbonate Gangue
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@jcg

Jcg·19 Jun 2026

Galena–Sphalerite Massive Sulphide Ore in Quartz-Carbonate Gangue

AI-suggested ID

Genaro Codina, Mexico

The collector's epithermal Pb-Zn-Ag vein interpretation is well supported. The banded colloform quartz-carbonate gangue is a hallmark of epithermal vein fill. The dark metallic mass is most likely galena ± sphalerite. Check for perfect cubic cleavage on a fresh break and test heft — galena is extremely heavy (SG ~7.6).

oreEpithermal

Formation

Epithermal low- to intermediate-sulphidation vein system; sulphides precipitated from hydrothermal fluids in fractures at shallow crustal depths (<1.5 km), with quartz-carbonate gangue banding indicating episodic fluid pulses.

Geological origin

Betaza Grande (Beta Grande) district, Oaxaca, Mexico

Properties

color

dark grey metallic with white gangue

grade

Unknown — visually high-grade sulphide zone

gangue

Quartz, calcite/carbonate — white botryoidal/colloform banding clearly visible

commodity

Lead, Zinc, Silver

host rock

Epithermal quartz-carbonate vein in andesitic or rhyolitic volcanic sequence

alteration

Silicic

Where else to find

Fresnillo, Zacatecas, MexicoTaxco, Guerrero, MexicoCoeur d'Alene district, Idaho, USAPotosĂ­, BoliviaCerro de Pasco, Peru

Suggested tests

  • • Heft test: galena is extremely dense (SG ~7.6); pick up the specimen — if it feels surprisingly heavy for its size, galena is confirmed
  • • Break a small piece and look for perfect cubic cleavage faces reflecting light — diagnostic for galena
  • • Streak on unglazed porcelain: galena gives grey-black streak; sphalerite gives white to pale yellow; fahlore gives black
  • • Test with dilute HCl on the white gangue — effervescence confirms carbonate (calcite/rhodochrosite) gangue component

Could also be

Argentite/Acanthite-bearing galena ore - The collector reports a silver-bearing vein; argentite (Agâ‚‚S) commonly occurs with galena in epithermal Pb-Zn-Ag systems and is visually indistinguishable from galena at hand-specimen scale
Tetrahedrite-tennantite (fahlore) ore - Fahlores are common silver carriers in Mexican epithermal Pb-Zn-Ag veins and can produce a similar dark grey metallic massive appearance alongside quartz gangue
Pyrite-sphalerite ore - The greenish-grey speckled zones could represent sphalerite (dark) and pyrite intergrowths rather than galena; a common look-alike in polished or unpolished hand specimens
primary-ore-lead-galprimary-ore-zinc-sphimportant-source-silhistorical-pigments-collector-specimen-e
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