Friday, October 18, 2019

Low Sulfidation Epithermal deposits

Low Sulfidation (LS) Epithermal drivel 

Just a quick intro on LS-Epithermal vein deposits. Very simple, but there is a reason for this....

911 metallurgist has a great description of low sulfidation epithernal deposits here - link, from which are some important things to note (in general) about low sulfidation (LS) Epithermal deposits and districts:
  • There are often multiple, generally, parallel veins

  • That are associated with (normal) faults. In many districts, often there are blind veins (i.e. the veins don't outcrop on surface).

  • Ore-grade mineralization in a district generally occurs over a specific range*
  • Mineralization isn't distributed equally throughout the vein, but is found in  specific zones (ore-shoots)

*assuming no post-mineral faulting (e.g. San Dimas) or multiple mineralizing/stacked events (e.g. very large epithermal districts e.g. Guanajuato, +/- Valdecanas).

For exploration it is key to target this favorable horizon, as if you
  • Drill above = erratic occasional Au-Ag hits (but could see elevated As, Hg and Sb).
  • Drill below = may hit elevated base metal (Pb, Zn, Cu) grades and low/no Au-Ag (e.g. San Sebastian - Hugh zone (Hecla Mining))

So when you are looking at a company with LS-Epithermal projects you want to see:
  1. Land position - you want the company to control or have a good chunk of a district. There is no point getting to excited about a company with a small project as any decent mineralization will quickly leave the property.
  2. More veins = more potential for large tonnages and multiple ore-shoots (e.g. Las Chispas).
  3. Large vertical extent of high-grade mineralization - this is harder without drilling. Generally in LS-Epithermal deposits the bonanza zone is ~200m thick (bigger systems = larger vertical extents - Santo Nino vein, Fresnillo had a 3-400m vertical extent).

Rhys, D el al  (2017) - Gold’17 – February 2017 – Rotorua, New Zealand 82  l Structure of the Palmarejo Mining District


  1. Thanks for this overview.

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  3. Your content helped me a lot to take my doubts, amazing content, thank you very much for sharing.