Low Sulfidation (LS) Epithermal drivelJust 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:
- 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.
- More veins = more potential for large tonnages and multiple ore-shoots (e.g. Las Chispas).
- 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