How to Find Sapphires… sort of
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 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?
Well, actually, it was pretty fun, and the thrill of discovery is enough to outweigh the slight discomfort of cold fingers and feet! 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.
A sapphire is a variety of the mineral corundum composed of aluminium and oxygen. (Al2O3). It is very hard, and not always blue as the most famous gemstones are. It can appear in a range of colours including blues, greens, yellows, golds and reds. These last are commonly called ruby, but it is still also corundum). These varieties of colours depend on varying proportions of elements such as iron and and titanium.
Tasmania in well endowed with mineral deposits, and when it comes to gemstones the NorthEast is particular good. The rivers and streams 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 – “alien 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 river deposits of today (alluvial 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 the Mineral Resources Tasmania pamphlet –> http://www.mrt.tas.gov.au/portal/en/fossicking-areas-in-tasmania
Once you’ve selected a spot, you will want to be prepared- so bring proper gear such as gum boots, hip-waiters, and extra clothing for cold and wet conditions. And for the actual sapphire hunting, you will need a large prospecting pan, two sieves with coarse 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-grained 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 out 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” within 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 glimmer. Other minerals like cassiterite, red-brown zircon, and green chrysoberyl may also be present.
Final thoughts:
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, one of the tallest in Tasmania) and rivers full of sapphires! Well, maybe they’re not really full
I’m an exploration geologist, graduate research student (PhD) in earth science and mineral deposits, and a keen traveler of the world. I love to investigate and explore the natural (earth) science behind amazing places. With this blog I hope to share my experience as an exploration geologist and travels around the world, whether for fun or work, and reveal the not-so-commonly publicized background science about these places.
