John's New England Minerals and General Geology Blog: SCRUBBY GULLY, TORRINGTON NSW

SCRUBBY GULLY, TORRINGTON NSW

Scrubby Gully is located on the western side of The Torrington Pendant, where the Mole Granite intrudes the overlying sedimentary rocks. In many places the boundary is notable for the presence of silexite, essentially a topaz-quartz rock. See especially my earlier blog entry “Torrington – Essential Reading” as well as the various references mentioned in the blogs on downloading from DIGS and the ALF site. Scrubby Gully may be reached by following the Butler Mine road and then the Mystery Face road, which branch to the left several kilometres north of Torrington from the Silent Grove road. At the Mystery Face car park, the fence directly ahead marks the boundary between the Conservation Area and private property. Follow the fence to the left for 15-20 minutes until it descends into Scrubby Gully. The alluvial areas are marked by hatching on the adjoining map. (The Scrubby Gully Mine shown is a bismuth/tungsten/lead deposit.)

To the right (upstream) are the Scrubby Gully alluvial workings, dating from the 1870’s and 80’s. Large quantities of “tin” (cassiterite) were extracted from here and from the gully below (downstream of the boundary fence). From the 1960’s until now fossickers have visited this area in search of topaz, especially the sky blue variety, for which the locality is well known.

For details of the geology of the diggings, see TWE David’s 1887 memoir on the Vegetable Creek Tin Mining Field (pages 71 and 164 especially. This can be downloaded from DIGS. The Minerama books on Topaz and Beryl also contain useful information.

The topaz comes in two forms – very waterworn (like the tin) and scarcely worn at all, reflecting the two likely sources - the ancient alluvial deposits and vughs in the silexite and adjacent granite. Only a very small proportion is the desirable sky blue variety. Along with the topaz is black tourmaline (schorl) and the occasional sapphire and zircon (both very worn). Pale green beryl is also found as unabraided crystals, no doubt also derived from the same vughs and veins as the topaz crystals and the tourmaline.

Any place where sediment is accumulating in holes and cracks is worth investigating for these gems. Remember that beryl is not a dense mineral and does not concentrate in the sieve centres as the other minerals mentioned do.