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26th NZ Micro-mineral Symposium 2008

by Val Lear

The venue chosen for 2008 was the inexpensive outdoor education centre at Bannockburn - a beautiful spot near Cromwell, surrounded by mountains and in good Central Otago style it did snow on the mountains while we were there but the next day we had to watch for sunburn while we fossicked. Of course this is the heart of the old goldfields and today the heart of wineries and other fruit growing as well as not far from Macraes Mining.
Thirty six of us gathered this year and eight of these were North Islanders and four had come from Australia. Ted and Sue Wearden had also travelled a long way just to get to the Sydney airport and then had the trip into Bannockburn. With Queenstown so close by I'm sure they made the most of this trip. Unlike some other Australians (Phil and Sue Ericksson), the Weardens stayed loyal to the Micromineral cause and did not go to London to see Cliff Richard perform!

The atmosphere in the work room was a companionable buzz as most of us were now familiar with each other. In annual style Michael Hirst and Judy Rowe fought a battle in the auction for high stakes over a little blue cavansite which Sue Weardon had shown in the best New Zealand mineral competition.

The giveaway tables held many generous donations of material from well known New Zealand sites but there was also a large donation of mainly South Island materials from Graham Robertson, who now lives in Clydebut was a chemist in Invercargill when there was a great group of collectors there round Gordon Auton. Graham has recently suffered a serious stroke, but is making a determined recovery and managed to visit our meeting, but he feels it is time to send most of his minerals to good homes.

From a participant point of view the weekend ran like clockwork and I believe many thanks for this go to Ron and Sara Keen, Mick and Sue Mackenzie, Heather Muir and John Caygill, and Bev Peevers and others from the Otago Club. Probably others also but there was certainly no shortage of willing helpers. We enjoyed generous meals and the “classic Kiwi BBQ” saw us eating sausages, chicken, Paua (abalone) patties, whitebait fritters and much more. We had good enough nights in warm bunk rooms but I do think some of the taller participants might have had some hardship with rather short bunk beds. It wasn't so warm outside in campervans however , as it was a decent Otago frost one night.

Glen the kiteman made an appearance again but the story was that he was too much in need of putting his feet up with a good book and the wind wasn't right. But the rest of us didn't have time to put our feet up. If we weren't checking out the giveaways or working on our own material ( I did hear someone whisper they hadn't touched their microscope since last symposium), then we were taking part in competitions, or we were on a fossicking trip, attending the auction or listening to the speakers.

Competition Results-

TETRAHEDRON TROPHY for the Best NZ Micromineral.  Winner = Mat Singleton's cacoxenite on puriri wood
RUNNER'S UP TROPHY for 2nd place in the Best NZ Micromineral = Sue Mackenzie and Sue Wearden (a tie)
 
STAN ROWE TROPHY for Best Overseas Micromineral.  Winner - Yvonne Mackenzie's linarite
 
RUTH JACOBSON TROPHY.  Best find from 2007 Symposium field trip.  Winner = Sue Wearden
 
Joint Mineralogical Societies of Australasia Trophy for Best annual photo of a NZ Mineral.  Winner = Mat Singleton's calcite



Trips on offer this year were varied. The real fossicking trip was offered to just a few of the fittest (or I read bravest) who were able to find someone willing to take up a 4 WD that they didn't mind getting scratched a bit! This was to Buchan's Lode, to a small exploratory shaft high on the Carrick Range. A drive, then a climb carrying spades and picks. The farmer would only allow access for two vehicles. Stibnite was collected and may have some little green XL's I understood from the noises coming from Mat Singleton later. My reading suggests they should be more focused on the gold colour not green. Rod moaned loudly about his body for the rest of the day. Some of us went to Bendigo Historic Reserve to look at the old gold mining relics and some of us went looking for Miocene casuarina (sheoak) leaf and seed fossils and gypsum XL's in the nearby Kawerau River bank. Glen and I went up to the skifields to lookout and ogle at the schist until I discovered Glen had stood on my long distance spectacles.



Our speakers were as follows -

Royden Thomson, local consultant geologist extraordinaire. What a mine of information so to speak. Royden talked on the area's geology and mineralogy. I learnt that at Bannockburn we were sitting on lignite. The Dunstan Range is growing fast. The landscape around us was glacial terracing (when it wasn't mountains of earth moved by gold diggers) and the region was traversed by New Zealand's biggest river, the Clutha. Royden talked about the schist landscape, uncommon in the rest of New Zealand. As well he talked about the faults of the region including the one across Lake Dunstan about 700 metres north of the Clyde Dam and how this was structurally engineered. Royden was involved in this work at the time.

Daphne Lee, Associate Professor at the University of Otago, talked about the region's palaeontology sites. Some of this information is to be found in her newly released book Central Rocks – A guide to the geology and landscapes of Central Otago http://www.unibooks.co.nz/product_info.php?cPath=1126_1336&products_id=48883). Have you heard of Lake Manuherikia? It formed in the Early Miocene. What harvests of fossils are to be found and Bannockburn is one site of the old lake sediments - remains of fossil freshwater crocodiles, fish bones, scales and jaws, palms and gum trees and Casuarina http://www.royalsociety.org.nz/Site/publish/Journals/nzjb/1984/13.aspx). And more to be identified. Daphne has recently won funding for a new quite remarkable project for herself and students at a site with exceptional preservation properties. This is on a private site and just as well as it needs to be kept safe.

Russell Beck, former curator of the Southland Museum and currently a well know carver of pounamu http://www.donnsalt.com/DOCUMENTS/RUSSELL%20BECK.htm), gave us a rather beautiful personal history that captured his love of rocks and minerals from a young age and his links with early collectors such as Bill Watters and the late Ed Sixtus from Motueka.. Russell developed a love of identifying sources of rocks and minerals and this became a passion in relation to nephrite . He has tried to visit all the sources of nephrite on a world scale. He has learnt of the original uses of nephrite back 8000 years and he has learnt about the patterns of trade of one of the toughest materials on earth. We learned of Russell's remarkable tenacity in his quest to uncover the lost reef of Beryl crystals on Stewart Island. What a story!!! Then there was the search for large and beautiful quartz crystals on the Old Man Mountain Range. Another great story!!! A little aside – when I got home from Bannockburn I did a bit more unpacking as we have just moved house. I unpacked a very old bottle from Glen's family labelled bottle found on serpentine gold diggings on Old Man Mountain Range and the bottle identified as being handmade in 1860's.

If you weren't at Bannockburn you missed some great talks.

Symposium speakers: a summary

by Phil Andrews

Since this year’s Symposium was held in a region of uplifted schist it was appropriate that the first speaker, Royden Thomson, a consultant geologist, should outline the area’s geology, beginning with New Zealand’s place in the plate tectonics scheme of things. It is a region of faults, such as those that had to be considered in the location and design of the Clyde dam (which measures around 100m from top to bottom). This dam was built to accommodate a certain amount of fault movement from any “river channel fault” activity.

Much affected by glacial activity, parts of the region were then superficially altered by sluicing and dredging – the first gold sluice was developed on the Clutha River.



Two jars of mystery objects were passed around for identification, with participants invited to include the taste test. The items, for those who did not already recognize them, were afterwards identified as moa crop stones and moa coprolites (fossilized droppings).

At question time I learned that piemontite/piedmontite is probably metamorphosed rhodonite.

In a splendidly illustrated talk Daphne Lee spoke on Central Otago fossils of Early Miocene age, found in an area of former lakes, collectively termed Lake Manuherikia. This was before the present mountain system had been uplifted, around 20 million years ago. Fossils found include gum leaves, ferns, Casuarina leaves, freshwater crayfish, freshwater shellfish (Hyridella), a 1cm-long fish jaw from an ancient Galaxias or whitebait, a thumb-nail-sized scale suggestive of the Murray cod of Australia, the scale of a bully dish, bird bones of diving petrel, six species of ducks, rails, seagulls, wading birds, parrots, nightjar owlet, magpie, pigeon, and possibly flamingo, as well as remains of bat and a rat-like mammal.

More particularly we were told of a Miocene-aged maar (an explosion crater filled with water, first recognized and named in Germany). The sediments of this former Central Otago maar (location left vague for its protection), have yielded to researchers a fascinating variety of fossils, including diatoms, sponges, fish, leaves (some insect-damaged) and insects. Here was made the first discovery in the world of the fossil leaves of orchids.

The speaker on the following night was jade carver Russell Beck (remember his first book, New Zealand Jade: The Story of Greenstone ?) http://www.nzbooksabroad.com/gbdetail.php?a=0-7900-0863-7&UID=&b=G7¤cy=NOK&x=Mana%20Pounamu:%20New%20Zealand%20Jade) Russell gave us an entertaining account of beryls and quartz, two true tales in one. An elusive beryl location in Stewart Island was first mentioned in the 19th century but had not been found since, until Russell set about searching, eventually relocating it in a near-shore reef. The quartz cluster which he had first seen and admired as a young man featured in his other story. In time he managed to buy this slab (which he brought along to show us) and he set about tracking its origin. Former family owners thought it came from Cornwall, but Russell’s study of the cluster’s associated minerals revealed that it had come from the Carrick Range.

Field trip report

Buchan's Lode, Bannockburn, Central Otago,

By Rod Martin
Map Reference: 45°6'38"S , 169°5'2"E



Eight of us made the trip up to the locality in two FWD vehicles and passed a number of gold prospect mullock heaps on the way up through the ranges. A light fall of overnight snow and the resulting meltwater had made the upper reaches of the track difficult so we walked the last section to the lodes.



The lodes were discovered by a Mr Buchan in 1874 and had been bulldozed open probably in 1979. There was abundant float of massive stibnite scattered around but the best material was associated with a hard chert. These were the only pieces that appeared to have any voids in which small stibnite needles could be found. Good specimens were also collected of massive stibnite showing slicken-sides although much of this was weathered.



Much of the stibnite is altered as described above by Ashley and Craw (1995) but a literature search did not produce any positive ID of the alteration products. The low rainfall regime and cool winter temperatures have produced an environment in which it is possible that many of the more mobile elements could have been retained in the alteration minerals and 7 or 8 distinct phases can be seen. Past assays of the stibnite show low gold values but arsenic is present locally to >5,000 ppm.

On our way back down we stopped to examine the mullock from one of the old gold prospects but only John managed to fight his way through the briar rose and matagouri to get to the main dump. There was little of interest there but a few samples were found of massive quartz, some of them with obvious sulphide banding.

If you enter the co-ordinates for the prospect into Google Earth then you can clearly see the three bulldozer cuts that were made along the faults.

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