File:Pyrite-bearing hydrothermal vein (mine near Joachimsthal, Bohemia).jpg

English: Pyrite in hydrothermal vein rock from Bohemia.

The town of Joachimsthal in Bohemia became rich and famous starting in the early 1500s from the discovery of silver-bearing veins in the surrounding hills. A silver mining boom followed - the silver was used to make coins named after the town - Joachimsthalers, or "thalers" for short (see: www.flickr.com/photos/vitenskapsmuseet/19962171845 ). This is the origin of the word "dollar".

The Joachimsthal area has a complex mix of metamorphic and igneous rocks. The most productive set of veins is oriented ~north-south. Other veins sets in the area are oriented east-west and northwest-southeast. A few are oriented northeast-southwest.

Vein mineralization occurred in multiple phases over long periods of geologic time. The most important phase was the so-called five-element mineralization, which involved the crystallization of silver, bismuth, cobalt, nickel, and arsenic minerals (plus uranium minerals). This five-element mineralization has occurred elsewhere, for example the Great Bear Lake area (Northwest Territories, Canada); the Cobalt, Ontario area; the Zimmer Lake area (Saskatchewan, Canada); and the Karuizawa Mine area (Japan).

In this sample, native silver occurs as clumps of tarnished, twisted wires (see nearby pictures in this photostream). The brassy areas in this photo are pyrite. The age(s) of polymetallic mineralization in the Joachimsthal area is not well constrained, but apparently occurred at Cretaceous-Tertiary boundary times.

Locality: unrecorded/undisclosed mine near the town of Joachimsthal (Jáchymov; Jachymov), Bohemia, northwestern Czech Republic

---

Geologic info. mostly synthesized from:

Ondrus et al. (2003) - Geology and hydrothermal vein system of the Jáchymov (Joachimsthal) ore district. Journal of the Czech Geological Society 48: 3-18.