Granite and it's association with Pegmatites

Hey fellow searchers,

I am doing some reading on Granite and it's association to Pegmatites and Veins of sought after gems.. This is as a direct result of watching Prospectors on Foxtel and reading more about what Mt Antero in Colorado is made up of, and what makes it such a popular area for finding gemstones.

What can anyone share on this interesting phenomenon and relationship?

Cheers,
Mark

The main gemstones found in pegmatites that I have come across are beryl crystals (mainly non gemstone quality), garnets and tourmaline crystals, mainly the black Schorl type crystals. Not far from Alice Springs in the Lander River area, you can find large outcrops of pegmatites in the hills with some of the biggest tourmaline crystals you are ever likely to come across. Some of these are like 10-15cm across and can run to over a foot long or larger/longer in places, unfortunately most are still in situ in the pegmatite, and cannot be removed with out damaging the crystals. Other pegmatites occurring in the valleys, mostly under cover, have produced lovely blue/green tourmalines, other pegmatite associated minerals included cassiterite (tin).

The coloured tourmalines are a lot rarer, with some being of gem quality. The pegmatites are mainly composed of similar minerals found in the granite source rock, including feldspar, quartz, mica etc. Most are derived from granite intrusions, but also rarely form through remobilisation of fluid through metamophic prosesses on other source rocks like gneiss. Various elements tend to be enriched in the pegmatites, resulting in the formation of the above mentioned crystals.

Here are a few pics of specimens I have collected from the NT and the Adelaide Hills, the bottom photo has tourmalines occurring in a micaceous host rock from a small pegmatitic intrusion. The top few pics are of mostly green tourmalines, some with partial blue colouring (bit hard to see in photo), the rest are common schorl tourmaline (black):

A pegmatite dyke up to 1 m wide intruding the You Yangs Granite is exposed in outcrops and shallow pits adjacent to Granite Road (AN2 on map). The full extent of the coarse grained area is not known. Quartz and feldspar crystals up to 6 cm in length occur in the pegmatite.

That's brilliant Goldpick, great response and very interesting story/findings.

Thanks for posting.

Nice one loamer, that's the article I read

I'm going to take a look there tomorrow...

Goldpick it is great to see some specimens from the Territory