Bowdens Silver

A shallow system, frozen in place

Bowdens sits in volcanic rocks east of Mudgee, and it is an epithermal deposit in the most literal sense: it formed near the top of a hydrothermal system, at low temperature and shallow depth, where rising fluids cooled and dumped their metal load.

The GSNSW record classes it as intermediate sulfidation — the middle ground between the acid, sulphur-rich high-sulfidation systems and the neutral, metal-poor low-sulfidation ones. That middle ground is where silver likes to live, and Bowdens is one of the largest undeveloped silver deposits in Australia.

Silver you cannot see

This is the part worth knowing before you look at core. The silver at Bowdens is not sitting there as shiny native metal. It is locked in acanthite and in silver sulphosalts — minerals that are dark, fine-grained, and thoroughly unremarkable to the naked eye. They travel with galena, sphalerite, pyrite and arsenopyrite.

So the visible sulphides are a proxy, not the prize. The galena and sphalerite you can see are telling you the system delivered base metals here; whether it also delivered silver in quantity is a question the assay answers and your eye does not.

Read the alteration, not the metal

The more useful signal is the clay. GSNSW logs the alteration at Bowdens as potassic, argillic and advanced argillic — a sequence that tracks increasingly acidic, increasingly hot fluid. Advanced argillic assemblages mean you are near the throat of the system.

Add a caldera structure and gangue that includes rhodonite along with carbonate, clay and quartz, and you have a deposit where texture does the talking: disseminated, veins, breccia fill and stockwork, all of which are ways of saying the rock was repeatedly broken open and re-cemented while fluid was moving through it.