Stephanie Sykora


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.


icon light bulb Exploring The Earth

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 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. Good luck!

 

The Pillars at the Bottom of the World

When it comes to pockets of land, they are far and few in-between in the remote south. Before you hit Antarctica the closest you’ll get is the southern tip of South America, the last gasp of south island New Zealand, and third, the Australian island state of Tasmania.

Having recently temporarily relocated to this island for university, I’ve noticed how its southern isolation results in bizarre and spectacular weather patterns. The locals say you get four seasons in one day, with chilly Antarctic winds howling from the south and warm high pressure systems creeping from the north. Because the island is so far south, making an effort to get out to the very southern-eastern tip of the island, as I did on a short trek to Cape Raoul, is worthwhile in and of itself.


 


 

Once there, however, a spectacular geological wonder awaits, and is a reward in and of itself! Giant sea columns riddle the shoreline, and although these columns may not be rare to Tasmanians, they are a wonder to be seen by any foreigner and worth a little explanation on how they formed and their geological ties to Tasmania.

The coastline of the southern Tasman Peninsula is composed of  giant dolerite sea columns that protrude up to 300 metres from the sea. The distinct elongated shape are the property of the dolerite; a mafic (oceanic) rock that intruded beneath the surface of the earth as sills (parallel to the bed)  or as dykes (across the bedding planes).

The hexagonal, prismatic column shape is termed columnar jointing. Dolerite forms this way because the magma cooled from the outside toward the centre surrounded by more or less consistent temperatures. These joints radiate outward from the centre of each column, which themselves form perpendicular to the flow base of the source magma (or lava if the rock was extruded at the surface, such as basalt).

A column can be broken into three sections; a lower and upper colonnade that from via conductive cooling, and a middle entablature that formed via rapid convective cooling (Spry, 1962; McPhie et al., 1994). This characteristic shape and orientation of columnar jointing provides a useful indication of where any feeder pipe for the dolerite would have been located, which in the southern Tasman Peninsula appears to be due north of Cape Raoul (Leaman, 1999).


 


 

While dolerite sea columns do exist elsewhere in the world,  Tasmania has the largest number of exposed columns. These intrusions were likely formedin the Jurassic, ~185 million years ago, at two kilometres  depth, from a massive volcanic event that covered up to a third of Tasmania, intruding into older sedimentary rocks.

Since then, the Tasman Sea and Southern Ocean have formed, and in the last 10 million years (Tertiary), rocks were exhumed by uplift and erosions, brought to the surface to experience breaking and cracking due to the elastic stress relief (Leaman, 1999). Consistent abrasion from the sea has undercut and shaped these spectacular cliffs to what we see today. The cliffs would have been even more spectacular as well, if the Navy didn’t at one point use the Cape Raoul columns as target practice!”

To me, what’s most striking about these bastions of southern Tasman Peninsula is how they protrude from the sea in almost perfect geometric shapes. Usually rocks and sea landscapes have been rounded and eroded to beautiful but odd and mismatched shapes. Even with millions of years of harsh conditions the columnar joints of the Tasmanian dolerite remain prismatic hexagonal pillars. Maybe this is a bit of my love for math coming through, but something about symmetry within nature always impresses me. These dolerite sea columns provide evidence of a major geological event, and are a must-see feature of the Southern Tasmanian coast.


 

Seals at the base of the pillars of Cape Raoul - by Stephanie Skyora

Seals at the base of the pillars of Cape Raoul – by Stephanie Skyora


 

Reference list available on request.