File:Breccia (hydrothermal vein rock from mine near Joachimsthal, Bohemia).jpg

English: Breccia 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). This photo shows breccia, a mix of large angular fragments surrounded by finer-grained material.

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

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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.