How to find sapphires… sort of [Northeast Tasmania]
Intro: I’ve never considered myself to be much of a rock hound, but being a geologist I guess I’m naturally attracted to pretty rocks and minerals… and so up sparked an idea to go panning (i.e. fossicking) for sapphires with some other Geo-friends in northeast Tasmania. What could be more fun than paddling knee high in a cold stream during Tasmanian winter, vigorously looking through sand for gemstones right? Well, actually, it was pretty fun, and the thrill of discovery is enough to outweigh the slight discomfort of cold fingers and feet! With this blog post I hope to share my attempts and luck at getting sapphires, and give you not only the details about how to pan for sapphires, but a little background on what they are and how they got to where they are today, waiting to be found… sort of.
Science Spiel: Sapphires; gotta catch ’em all (Geology, Mineralogy)
A sapphire is a variety of the mineral corundum (Al2O3). It is very hard, and not always blue with a range from blue, green, yellow, gold and red (which is commonly called ruby, but again, it is still the same mineral as sapphire; corundum). These varieties of colours depend on varying proportions of elements such as Fe and Ti.
Tasmania in well endowed with mineral deposits, and when it comes to gemstones the northeast is particular good. The rivers and stream have eroded sapphire-bearing rocks, such as massive basalt. The basalts themselves did not form the sapphires, but are the host as they brought xenoliths of rocks from a deeper, hotter source such as (tin-rich) granites (Bottrill, 1996/05). Once the sapphire bearing rock (i.e. granite, xenolithic basalt, etc.) was exposed to the surface, rivers eroded, transported, and eventually concentrated the sapphires into the alluvial deposits of today (i.e. river beds).
Alright, now on to prospecting!
Since concentrations of sapphire are found in stream banks and gravels, the first thing you have to do is find a location that is prospective. For more information on prospective areas in Tasmania, check out this pamphlet –> http://www.mrt.tas.gov.au/portal/en/fossicking-areas-in-tasmania
Once you got your spot, you will want to be prepared so bring proper gear such as gum boots, hip-waiters, clothing for cold and wet conditions. And for sapphire hunting, you will need a large prospecting pan, two sieves with course and finer mesh sizes, a shovel, a bucket, and a jar to put any treasures in.
Shovel the coarse sand from the river into your sieves or pan, and swirl it around with water. Once the fine grain sands are gone you will have concentrated the heavier rocks in the bottom center (from swirling) so flip your sieve or pan over and dump of the rocks onto another pan or on the ground. Then take a look!
A good indicator is the presence of black pleonaste spinel, known as “black jack” disseminated in the pan. The sapphires will be well-rounded grains, less than a centimetre in size. They are not gem quality in their rough form, so look close and hard, they will have a glassy to translucent appearance, with some showing a chatoyancy glimmer. Other minerals like cassiterite, red-brown zircon, and green chrysoberyl (green) may also be present.
So you might be wondering how I did? Well, I’m definitely not buying jet planes with my new sapphire fortune... We only found a couple small grains, but that might be due to the season. If possible, I recommend going in the spring, where the rivers are full and running fast and bountiful with new sediments. Northeast Tasmania is home to beautiful rainforests full of waterfalls (like St. Columbia Falls, the largest in Tasmania) and rivers full of sapphires! Well, maybe not really full of sapphires, but they are out there, and hopefully now you know a bit more about them and maybe how to find them for yourself. Goodluck!
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