Final Stay-at-Home Day, Monday 27 April 2020: Stone Thirty-Three

Today is New Zealand’s 33rd day at Covid-19 Alert Level Four, which is set to be lifted at 11.59 pm tonight. New Zealand has had clearly defined Alert Levels from the beginning, which has been very useful in shaping people’s expectations and ability to see things through. It was initially announced that the country would be at Alert Level Four for four weeks (two cycles of two weeks, two weeks being understood to be the incubation period for Covid-19). This has been extended for only a further five days before the country moves down to Alert Level Three for an intended two weeks. With a population of five million people, New Zealand’s highest official daily new cases of Covid-19 infection was 89 (reached twice, on 2 and 5 April). This dropped to 18 on 12 April and has been in single figures since 19 April. The daily level of hospitalisation due to the virus has been very low, usually less than 20 being in hospital at any one time. Sadly, 18 people with Covid-19 infection have died, all aged over 60, half over 80. Ten of the deaths came from one Aged Care Home in Christchurch. In total, New Zealand has officially recorded 1,470 cases of Covid-19 infection (as at 25 April). 

The final Stay-at-Home stone, Stone Thirty-Three, is a small polished jasper stone.

As befitting the occasion, this is a special stone. It is also an unusual one as it does not come from a beach but from many kilometres inland. I found a large stone embedded in a farm track near Waikaka in Southland, just north of Gore.  I hand-chipped Stone Thirty-Three from this larger stone, so it started off with sharp edges, requiring extra tumbling to smooth it out. Even then, some small rough patches have remained.

I told the story of the large stone in part of a previous Post Diane’s Stone, and an Introduction to Jasper. Here it is:

I once found a rock in a track on the farm I grew up on, “The Mains” near Waikaka. When trying to identify it, I thought first of all that it was chert but it turned out to be jasper (Minerals.net states that “when Jasper is dull and lacking interesting colors or patterns, it is not Jasper but rather Chert”). I eventually broke it up, with difficulty – to put it technically, jasper “fractures conchoidally” (like flint – Geology.com points out that jasper, chert and flint are very similar, all being varieties of opaque microcrystalline quartz). When polished, the pieces of the rock I found had a very glossy, almost waxy, quality. 

I later discovered that jasper is very common around the Waikaka area, being part of the gold-bearing quartz gravels of the area – see the Tumblestone Posts “Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka” and “Waikaka’s Auriferous (Gold-Containing) Quartz Gravels“.

Thanks to those who have been following this Series and I hope you have enjoyed meeting such a diverse range of stones from New Zealand’s South Island. It just remains for the final Stone of the Week to be named.

The next Post in this Series is Stay-at-Home Week Five, Final Stone of the WeekThe first Post is Stay-at-Home Day One, Thursday 26 March 2020: Stone One

Diane’s Stone, and an Introduction to Jasper

Just under a year ago, my niece Diane bought a new house in Christchurch. While doing work in the garden, she found a stone that she thought was potentially interesting. She showed it to me when I was visiting her and I recognised it as jasper. The stone was in a rough condition. It was far from smooth, and running through the middle was a brittle and pitted silica band. The photos below are of the stone after it was washed and allowed to dry:

I thought that tumbling it would at least bring out the colour, so I offered to take it away to work on it.

What is jasper? Jasper is a well-known red stone found on many beaches in New Zealand, especially in the South Island. I have found it on beaches like Birdlings Flat in Canterbury, and at Riverton and Gemstone Beach in Southland. It tends to stand out amongst other stones because of its deep red colour:

I once found a rock in a track on the farm I grew up on, The Mains near Waikaka. When trying to identify it, I thought first of all that it was chert but it turned out to be jasper (Minerals.net states that “when Jasper is dull and lacking interesting colors or patterns, it is not Jasper but rather Chert”). I eventually broke it up, with difficulty – to put it technically, jasper “fractures conchoidally” (like flint – Geology.com points out that jasper, chert and flint are very similar, all being varieties of opaque microcrystalline quartz). When polished, the pieces of the rock I found had a very glossy, almost waxy, quality. 

I later discovered that jasper is very common around the Waikaka area, being part of the gold-bearing quartz gravels of the area – see the Tumblestone Posts “Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka” and “Waikaka’s Auriferous (Gold-Containing) Quartz Gravels“.

In Riverton, outside the museum Te Hikoi, a number of rocks from Southland are on display. One of them is a large piece of rounded jasper. Inside the museum, a number of smaller jasper stones are displayed, including a dark green one.

When I recently visited Jack Geerlings in Winton, who has an extensive collection of stones and rocks from southern New Zealand, I noticed he had a number of pieces of jasper (see photos below). He had collected some from the Coromandel Peninsula, in the North Island, and generously gave me a piece. Outside his shed, where he had a number of rocks and boulders on display, a rock of red and green jasper can be seen. And inside his shed, he showed me a polished stone of orbicular jasper. In her book “Collecting Rocks, Gems and Minerals” (3rd edition, 2016), Patti Polk has an extensive section on different types of jasper. On pages 121 and 122, in her entry on orbicular jasper, she states: “Orbicular jasper is generally a type of highly silicified rhyolite or tuff that has quartz and feldspar crystallized into radical aggregates of needle-like crystals that form orbicular ir spherical structures.” The photos below include page 122 from her book, illustrating some of the variants of orbicular jasper.

To find out more about jasper, I consulted one of my books, “The Illustrated Guide to Rocks and Minerals” (2015) by John Farndon. On page 204, he notes that jasper is a red, green or yellow variety of chalcedony. Chalcedony arises when quartz crystals forms at low temperatures in volcanic cavities. The crystals can be so small that they are visible only when magnified, which is the meaning of the term “cryptocrystalline”. The general name for cryptocrystalline quartz (also called “microcrystalline”) is chalcedony, which comes in a vast array of colours and patterns. As Farndon notes, it includes blood-red carnelian, wine-red jasper, brown-banded agate, green-moss agate, apple-green chrysoprase, and black and white onyx. The colour depends on what minerals seep into the rock. The presence of iron causes the red colour in jasper. In fact, jasper is often referred to as a coloured form of opaque agate, agate being one of the major types of chalcedony (see, for example, the wikipedia entry on chalcedony).

Mindat.org has a lot of photos of different variations of jasper. Below are also photos of some different types of jasper, with the one on the right showing rough and tumbled stones.

To get back to Diane’s jasper stone: After tumbling for just over a week (9 days and 19 hours, to be precise) in 220 silicon carbide grit (along with other stones), followed by five and a half hours tumbling in water and sunlight soap, the stone’s colours emerged much more clearly. Nevertheless, it was still rough in places, with the middle band of silica especially pitted:

However, the stone showed promise. I next tumbled it in 320 silicon carbide grit for another week (seven days and one hour to be exact), followed by 21 hours in sunlight soap. There was a small improvement in the surface condition of the stone, though of course the pits in the middle silica band were too deep to erode away:

I next tumbled the stone in pre-polish tin oxide for five days, followed by a 21 hour soap tumble. Then it spent nearly 12 days in pro-polish tin oxide, finally spending just over four days in a borax burnishing tumble. Unfortunately, these stages seemed to bring out various lines of weakness in the stone, and it failed to take a polish. I didn’t think that further tumbling would improve it:

While I found this disappointing, it is not unusual for some jasper. Many of the jasper stones found on the beach have a chip out of them or some kind of crack. There is often a brittleness in jasper that gives rise to this. 

At least Diane now has a much cleaner and more colourful stone.

Twelve Stones, Part One

I recently presented 12 of my polished stones to a work colleague in appreciation. 

zDSC01427

I took on the job of Assistant to an AB Technician in the dairy industry for three weeks, at the height of the insemination season. This was a completely new experience for me and I enjoyed it a lot, largely due to the support and patience of Tony, the Technician I was assisting. I chose to give him 12 stones because I spent a lot of time preparing the 12 inseminator implements that he regularly used. Below is a photo of inseminators being loaded (a straw of bull semen is loaded into the end of each inseminator, its plug snipped off with scissors, then a plastic sheath is threaded over it to hold in place).

aaa

These are the twelve stones:

1-6 stones 2227-12 stones 222

I am taking the opportunity in this Series of Posts to dig into aspects of different types of stones and the places from which they were collected. This first Post will describe Stones #1 to #3, with the rest dealt with in Parts Two, Three and Four.

1) Stone #1 Dark Red Jasper

I found a rock in April 2016 near Waikaka in Eastern Southland. It was embedded in a farm track on “The Mains”, the farm on which I grew up. Red Jasper is a rock to be found as part of the Waikaka quartz gravels which contain the gold mined in the area between the 1880s and 1920s. There is an old gold dredging pond about 100 metres north of the track. I extracted this large Jasper rock and took it home with me to Karapiro on the plane. Later I broke off a few pieces to tumble-polish. Due to the brittle nature of the rock, I did not completely smooth the stones out before their final polish. (Click on the photos below to view them and see their accompanying captions.)

Location of Waikaka at the bottom of the South Island (source: Google Maps):

Waikaka location

More on Jasper as a gemstone.

Other TumbleStone posts referring to “The Mains”: Maps as a Resource: New Zealand’s “Maps Past”, Part OneMaps as a Resource: New Zealand’s “Maps Past”, Part TwoJasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka; and “You run from the river, when it long ran over you…”

2) Stone #2 Granite or Basalt Porphyry, containing Feldspar Crystals

I found this stone at Riverton, Southland, in September 2018. This type of stone, while not numerous on Riverton beaches, is not rare and one is likely to be found within 10 to 15 minutes of searching. Its most obvious and interesting characteristic is the lighter-coloured feldspar crystals packed into the darker surrounding matrix. This indicates the stone is of volcanic origin, and is probably either basalt or granite. “Porphyry” is a term for the texture of an igneous rock consisting of large-grained crystals, such as feldspar or quartz, lodged in a fine-grained silicate rich matrix. These crystals formed within magma underground – this material then reached the earth’s surface and cooled relatively quickly, “trapping” the crystals in fine-grained rock. The crystals can vary in size, as shown in these three photos from the Riverton Museum “Te Hikoi” (these photos were taken with the permission of Museum staff in December 2016):

The Riverton Museum often has a display of local stones types, usually set up for children. The well-known geologist Hamish Campbell has been instrumental in putting this together. In 2017, the Museum developed a five-page pamphlet as a guide for children and families to collect nine different types of stones from the area between Riverton and Orepuki.

Rock Type 1 “Volcanic Rocks” would include Granite and Basalt Porphyry. Reference.com provides the following explanation of the differences between Granite and Basalt: Granite is an intrusive rock that is formed when magma cools inside the crust. This slow cooling gives time for crystals to grow, making it more coarsely grained than an extrusive rock, formed at the earth’s surface. Basalt, on the other hand, is an extrusive rock, with a smooth texture from rapid cooling, usually by water. Granite has a high silicon content; it is mostly made out of quartz, mica and feldspar. Basalt contains more calcium oxide, manganese oxide and iron compounds than granite. I am unable to exactly identify Stone #2. Granite stones can easily be found in the Riverton area (see Stone #4) but Stone #2 seems to be less coarsely grained than Granite.

Location of Riverton (source: Google Maps):

Riverton location

3) Stone #3 Unknown Variegated Green Stone

This stone, found at Riverton in February 2018, is darker green towards the thicker end, with the other end being a lighter green. When slowly rotated in the light, small specks of mica can be seen at the darker end. It is probably a metamorphic stone having been subject to significant heat and pressure at some stage. So I looked up metamorphic rocks in “A Photographic Guide to Rocks & Minerals in New Zealand” (2011), written by Nick Mortimer, Hamish Campbell and Margaret Low. Page 20 (see below) has a basic classification which led me to consider whether at least part of this stone could be “Hornfels”. Page 119 (also see below) mentions that Hornfels contains “small micas” and that some occur in the Bluff area, which is along the coast not far south-south-east of Riverton. 

Many of the stones on Riverton beaches are thought to have come down the Waiau River whose mouth is about 50 kms westwards.

Stones are often unique in their shape, size and patterns, and contain a range of elements, layers, intrusions and so on, which make them very difficult to identify with certainty. Chemical analysis is often needed. Stone #3 remains unidentified.

Stones #4 to #6 are described in Part Two.

Maps as a Resource: New Zealand’s “Maps Past”, Part One

Over the past few months, I have been doing some research on the district in which I grew up, around Waikaka in Southland, and on the members of my family who first settled there in the 1870s and their involvement in farming and gold dredging. This is an area I return to from time to time, and from which I collect stones. Recently I have been seeing what is available online in terms of historical maps. One very useful website I have discovered is “Maps Past”  http://www.mapspast.org.nz which, oddly enough, does not have a page giving details of who has produced the site.

The opening page of “Maps Past” presents a map of New Zealand, and it is possible to zoom into any particular part of the country. Then you are able to click on different dates (set as decades, starting at 1899 with only 1939 not available) and bring up maps from that time of the area on your screen. Sometimes as you go from one decade to another, the same map will be presented, depending on when new maps were constructed. I will illustrate this by showing the different maps available for Waikaka and the area to the south which includes “The Mains”, the farm on which I grew up. 

There are nine different maps that are available for the Waikaka area, one of which is a recent aerial photo. The following are thumbnails that will expand when clicked on (there is a “View full size” underneath the expanded image in the viewer – you may need to scroll down to see it):

This first part of this Topic will deal with the first four of these maps. The other five are dealt with in Maps as a Resource: New Zealand’s “Maps Past”, Part Two. Note that the following map images are not expandable – use the thumbnail above for a more detailed view of any of the maps.

The first map is for the decade ending in 1899. It is actually from a map of the Chatton Survey District published in 1888:

001 - NZMS13 1899

It is interesting to note the areas around Waikaka designated as “Auriferous Reserve” and “Gold Reserve”, and the area of dots to the southeast of the town labelled “GOLD WORKINGS” (though it is very difficult to see this label). Gold had been discovered near Waikaka in 1867 and the following 60 years saw various phases of panning, mining, sluicing and dredging. Section 30 of Block 3, located directly south of Waikaka, just below the centre of the map, was bought in April 1876 by Hugh Paterson, my great-great-grandfather. This was the beginnings of “The Mains” farm.

The second map is for the decade ending in 1929. It is actually from a map of the Chatton Survey District published in 1929:

002 - NZMS13 1929

One noticeable addition to the map is the Waikaka Branch Railway, constructed in 1907 and 1908 to provide faster transport of agricultural produce to markets. It was the last of the branch lines authorised in northern Southland. In “Waikaka Saga” (1962), Evans refers to James Paterson, my great-grandfather, as one of the “well-known characters” (page 191) on the train, one of the local land-owners who traveled to Gore (about 25 kms away) on Saturdays to do business. “All of these men were intensely interested in politics, religion, world affairs, agriculture, and so on. Even before the train had pulled out of Waikaka station, the argument had started and they had forgotten to buy their tickets, and so scrambled on at the last moment…[They] used to have great arguments and discussions on the train, so much so that it became quite an institution.” The railway line ran through “The Mains”, with the Pullar Railway Station (Siding) located just on the southern boundary of the farm. It is reported in the Mataura Ensign on 27 July 1909 that James Paterson was given 50 acres of the Waikaka Commonage (mining reserve) to compensate for part of The Mains being cut off from access to water. Due to competition from roading, the Waikaka Branch Railway closed on 9 September 1962 (Wikipedia). 

In the middle of “The Mains” was a rail bridge across the “Waikaka Stream”. Soon after the line opened, Leonard Paterson, my grandfather, traveled to high school in Gore by train which would slow down by this bridge so he could hop on (“Paterson Family Reunion 2002”, page 24). He was also a passenger on the final train from Waikaka in 1962, standing sixth from the right in the photo below, his wife Annie to his right. They had retired to live in Gore in 1957.

school centennial p71 last train
Source: “Waikaka and District Schools Centennial 1883-1983 Pictorial”, page 71

The third map is for the decade ending in 1959. It is actually from a map of the NZMS1 series published in 1946, the S161 “Heriot” Sheet. This is a topographic map, showing relief, using contour lines, whereas the previous two are land survey maps primarily concerned to present farm land boundaries. 

003 - NZMS1 1959

This is the same map with the approximate boundary (in black) of “The Mains”:

003 - NZMS1 1959 - Copy

Note that the road running east of the boundary of “The Mains” is called “Turnbulls Road” (after a prominent family) . In later maps this becomes “Turnbull Road”. Note also that “Tailings” are indicated in “The Mains” to the left of the railway line. Elsewhere on the map is reference to “Workings” and “Old Workings”.  These are old gold dredge tailings and sluicing areas. Most of the flat land along the west and east branches of the Waikaka Stream as far south as McNab (21 kms) was heavily dredged between 1896 and 1926. As reported in an entry on “Gold-Dredging in the Waikaka Valley” in “The New Zealand Mining Handbook” of 1906, “By means of a separating-box soil and sand are distributed over the tailings, which are left perfectly level, and when sown with clover and grass yield excellent grazing” (page 198).  In “Golden Reflections: A History of Waikaka Valley” (1992), J.F. McArthur reports: “Dredging operations disturbed the whole valley floor, which was completely turned over to the depth of 12 to 14 feet [3.7 to 4.3 metres]” (page 366). He refers to how the dredges lifted the top soil of the area about to be dredged and placed it, using an extended chute, over the area previously dredged (page 367). It has been claimed that much swampy land was improved considerably by gold dredging. Certainly I remember the tailings on “The Mains”, although prone to drying out in summer, provided great free-draining winter grazing and grew excellent lucerne (alfalfa). 

The fourth map is for the decade ending in 1969. The “Maps Past” website indicates this is based on the NZMS1 series “Heriot” Sheet published in 1957, again a topographic map:004 - NZMS1 1969

However, only parts of the railway line are indicated even though it was not removed until after 1962, when I remember my father dismantling the section that ran through “The Mains”. Maybe this is actually based on a later map. A new “Old Workings” label appears on the map to the south of “The Mains” boundary. These old gold dredge ponds on the Waikaka Stream existed even prior to the previous map.  I used to fish for trout there often as a boy, and we called it Turnbull’s Dam as it is located on Turnbull’s farm (even though it is a couple of ponds through which the river flows rather than a dam). It is interesting to note on this map that the road in the south-east corner is called “Sandy Knowes Road”. On later maps this becomes  the “Kelso Maitland Road” before becoming “Glenkenich Road”. Meanwhile, the road in the north-east is on this map called the “Waikaka Kelso Road” (the “Kelso” part can’t be read on this segment) and on the next map is called “Sandy Knowes Road”. (On all maps, “Garden Gully Road” connects these two roads.) There is potential confusion here for local historians when local people or documents refer to Sandy Knowes.

This Topic is continued in Maps as a Resource: New Zealand’s “Maps Past”, Part Two, where the next five maps are discussed. Another Post sets out Tips on Using “Maps Past” to assist you if you are not sure what to do to get started in using the website. 

Waikaka’s Auriferous (Gold-Containing) Quartz Gravels

I grew up at Waikaka in Southland, New Zealand, and was always aware that it was an area where gold mining had taken place in the past. The Waikaka River ran though our farm, and the river flats contained lots of small ponds that were referred to as “dredge ponds”. When I was young, I remember being shown a small bottle with a few flakes of gold that the family had. And when I did a biography of a family member in my second year at high school, I chose my great grandfather James Paterson who had been involved with gold dredging. I left Waikaka to go to University in 1974. I still visit the area from time to time, even though the farm is no longer in family ownership. The following is a report on one aspect of my recent research on the geology and history of the Waikaka district. Later posts will report on other things I have found.

“THE GEOLOGY OF NEW ZEALAND” (1978)

I now live near Cambridge in the North Island of New Zealand. On the second Sunday of each month, Cambridge has a “Trash and Treasure” street market. At September’s market, I came across a secondhand bookstall that had a copy of the large two volume “Geology of New Zealand” published in 1978 by the New Zealand Geological Survey. A bargain at $40, even though a little dated. Its strength is its detailed coverage of every area of the country. During the decision to buy it, I looked up a number of places to see what what information it had on them. In the section on Southland in Volume II, I unexpectedly came across reference to “Waikaka Quartz Gravel”, the first time I became aware that there was a special designation for the gold-bearing gravel so significant to Waikaka’s history. 

The authors state on page 524: “In eastern Southland the Waikaka Quartz Gravel com­prises mainly quartz gravel and clay, but includes fragments of strongly leached pale blue or white schist or greywacke; these were either derived in their leached condition from the deeply weathered zone under the mid-Tertiary beds, implying local erosion and unconformity under conditions of low relief, or leached after deposition, implying a continuation in this district of peneplain conditions into the late Tertiary; probably both events occurred.”

THE NEW ZEALAND STRATIGRAPHIC LEXICON

Back home, I did an internet search for “Waikaka quartz gravel” and discovered that the New Zealand Stratigraphic Lexicon includes a brief entry on “Waikaka Quartz Gravels” (http://data.gns.cri.nz/stratlex/view.jsp?id=3492).  This Lexicon, operated by GNS Science, is a list of official and recognised geological terms and units. GNS Science is a New Zealand Crown Research Institute for geology, geophysics, and nuclear science. As is stated on the home page of the New Zealand Stratigraphic Lexicon, “Precise definitions of units of rock and periods of geological time are required, especially for mapping and study of geological history…This is a list of New Zealand rock unit names, giving information on age and distribution, the hierarchy of stratigraphic units, synonyms, and references to relevant literature” (http://data.gns.cri.nz/stratlex/index.jsp). 

The listing of “Waikaka Quartz Gravels” in the New Zealand Stratigraphic Lexicon provides no information on it but it means that this geological feature has official recognition, reflecting its prior appearance in geological studies. The two important prior sources noted in the Lexicon entry are the one I have already mentioned above – page 534 of Volume II of “The Geology of New Zealand” – and the research undertaken in the late 1940s associated with “The Geology of the Gore Subdivision, Gore Sheet District (S170)”, published in 1956 by the Department of Scientific and Industrial Research as New Zealand Geological Survey Bulletin 53. This is for sale as a pdf file for $20 from the GNS Science Online Shop. 

“THE GEOLOGY OF THE GORE SUBDIVISION” (1956)

“The Geology of the Gore Subdivision” (1956) contains interesting information about the Waikaka quartz gravels. For example, pages 9, 14 and 15 contain the following points: the gold to be found in the area is very fine; the early 20th century saw a lot of gold dredging, with most of it in the valley of the Waikaka River; geologists referred to gold-bearing quartz around Waikaka at the end of the 19th century; the existence of lignite (“brown coal”) is also noted (this was an important fuel to operate the gold dredges); and the gold is noted as likely deriving from the mica schist further north in Otago, perhaps from the wave action of ancient seas or from the eroding action of rivers.  

As an aside: The Department of Geology at the University of Otago notes that the existence of gold deposits in Otago schist is an example of “mesothermal” gold. These deposits are formed by hot water moving through rocks which are uplifted from deep (10 km) in the Earth’s crust. The gold in the deposits are extracted from the surrounding rocks by being dissolved in hot water. It is then deposited in the schist by sudden cooling or changes in pressure as the waters are forced through rocks by earthquakes. The gold deposits occurs within small quartz “reefs” or veins in cracks in the schist.  I would guess that it is such deposits that have been broken down by water action in ancient oceans or rivers south of the main Otago schist area, finding its way as very fine gold into river valleys like that of the Waikaka. This is alluvial gold found in association with quartz gravel washed out of schist bedrock, the basic constituents of the Waikaka quartz gravels.

In Nick Mortimer, Hamish Campbell and Margaret Low’s (2011) “A Photographic Guide to Rocks and Minerals of New Zealand”, it is stated that gold “is concentrated by ancient hydrothermal systems into quartz veins or lodes in igneous and metamorphic rocks such as rhyolite, granite and schist” (page 46). When rivers erode these hard rock deposits, the gold is freed as individual grains.  The rivers  can then concentrate the gold in loose river gravels or “placers”, hence the term “placer gold”.

In pages 93-100 of “The Field Guide to New Zealand Geology” (2003), Jocelyn Thornton describes the “Haast schist region” (see below). The southern edge of this region lies just to the north of Waikaka. 

schist in Thornton
Top of page 93 of “The Field Guide to New Zealand Geology” by Jocelyn Thornton, 2nd edition, published in 2003

Schist is a metamorphic rock that develops under the weight and pressure of overlying sediments. Mica, a shiny flake, grows in pressurised rock and can commonly be found in Otago schist. Mica and other flat mineral grains align to give schist cleavage, foliation and splittability. A good example of schist and its use is Mitchell’s cottage at Fruitlands in Central Otago. This building made of schist was erected between 1880 and 1904 by Andrew Mitchell, a gold miner and stonemason from Shetland. The photo below is of the cottage in its setting in the schist landscape.

mitchells cottage schist landscape
Mitchell’s Cottage, Central Otago – a schist building in a schist landscape. Source: https://www.flickr.com/photos/brian_robinson_nz/16620373332

Quartz veins bearing gold can be found throughout the Haast schist region. “There must have been a long-lasting fluid flow through the buried schists. As pressure and temperature increase, minerals that contain water in their structure will lose the water and this water will move up through the pile from the deepest hottest parts, leaching even trace elements [like gold] from the rocks and concentrating them in veins” (page 99 in Joyce Thornton’s, 2003, “Field Guide to New Zealand Geology”). Schist, when weathered or eroded, tends to eventually break down into fine clay. 

WAIKAKA QUARTZ GRAVELS DEFINED

Back to “The Geology of the Gore Subdivision” (1956)… On pages 16 and 17, Table 5 sets out the main stratigraphic units of the area, arranged in terms of geological age. As shown on page 16 (see below), the Waikaka quartz gravels are grouped with the very similar Waimumu quartz gravels (Waimumu lies about 35 kms south of Waikaka, not far from the Mataura River south of Gore) and are described as follows: “Dominantly subangular to rounded white quartzite pebbles, rare quartzite red jaspilite and decomposed schist, in a micaceous clay matrix. A fluviatile deposit on a land of low relief but not a peneplain.”

Geol Gore Subdiv p16
Page 16 of “The Geology of the Gore Subdivision” (1956)

The next six paragraphs break down and interpret this description of Waikaka quartz gravels: 

Dominantly subangular to rounded white quartzite pebbles = This refers to roundness, size and type of the most common stone. Geologists often work with six categories of roundness for stones, going from sharp and jagged to smooth and round – 1) Very angular (where corners sharp and jagged),  2) Angular, 3) Sub-angular, 4) Sub-rounded, 5) Rounded, and 6) Well-rounded (where corners are completely rounded). Geologists usually also categorise stones in terms of size. One set of categories is as follows: A “grain” (e.g., of sand) has a diameter of 2 to 4 millimetres, a “pebble” is between 2 and 64 millimetres,  a “cobble” is 64 to 256 millimetres in diameter, and a “boulder” is larger than that. [Note that “gravel” is a loose collection or aggregation of stones which can be of various sizes, though it is often of pebbles mixed with granular material and may contain larger stones as well.]

Quartzite is formed when a quartz-rich sandstone has been exposed to high temperatures and pressures which fuse the quartz grains together forming a dense, hard rock. Quartzite has a high degree of hardness as well as a high quartz content. It generally comprises greater than 90% percent quartz. Quartzite also tends to have a sugary appearance and glassy lustre. The purist quartzite is white in colour (and we often simply refer to it as quartz), though quartzite can be of a variety of colours dependent on minor amounts of impurities being incorporated with the quartz during metamorphism.

Quartzite red jaspilite = Jasper is an aggregate of microgranular quartz and/or chalcedony and other minerals. It is an opaque, impure variety of silica, usually red, yellow, brown or green in color. The common red variety of jasper is due to iron inclusions. Jaspilite is a banded rock made up of layers of jasper with other material, such as hematite and quartz.

A micaceous clay matrix = This is a fine-grained mass of material, predominantly clay, with fine scales of mica present, this clay and mica coming from the break-down of schist, as noted previously.

A fluviatile deposit = This means “of, found in, or produced by a river”.

A land of low relief but not a peneplain = A peneplain is a gently undulating, almost featureless, plain that is produced by river erosion that would, given enough time, reduce the land almost to sea level, leaving so little gradient that essentially no more erosion could occur.  An area of low relief is one that tends to be flat but is not completely flat, having some slope to it (and therefore not being a peneplain). 

WAIKAKA QUARTZ GRAVELS ON THE MAP

“The Geology of the Gore Subdivision” (1956) contains a geological map. Right at the top margin is the southern part of the Waikaka district, with the Waikaka township two miles (just over 3 kms) north of the map border. A section of Waikaka Quartz Gravel is shown on the eastern side of the Waikaka River, starting just south of Fleming and extending northwards as a narrow band, coinciding with the river terrace. There are also three outcrops noted on the western side of the Little Waikaka River, not far from what is locally known as the Queen Hill on Turnbull Road. 

The nearby river flats are classified as “river alluvium” and the ridge in between consists of “Gore Piedmont Gravels”, defined in the Key as “deeply weathered rusty brown auriferous quartz-greywacke gravels”.  This suggests to me that the Waikaka quartz gravels are a series of beds, overlain by more weathered gravels, which they may be the source for, and they are probably also one of the main sources of the river flats alluvium which will no longer have the clay matrix of the beds. It also means that gold is to be found not only on the river flats but also above the river terraces – which is why sluicing was used by miners in this area.

 

 

 

 

 

 

Jasper Stones and Petrified Wood, Shepherd’s Creek, Waikaka

In the last week of July 2017, on a visit to Southland, I decided to take a look at what stones I could find along a small stream near the Waikaka Primary School, the school I had attended when I was a boy. This stream called Shepherd’s Creek, enters the Waikaka River about 4 kms (2.5 miles) further south, on the farm I grew up on, “The Mains”. 

Below is a map of the location of Shepherd’s Creek near Waikaka School (Google Maps, satellite view) – The Creek is in blue, the area where I looked for stones in July 2017  is outlined in black:

S Creek School aa

Below shows where Shepherd’s Creek (blue) joins the Waikaka River (purple), on “The Mains”, the Paterson family farm where I grew up (the northern boundary of the farm is outlined in the black dashed line):

S Creek Mains lge yy

My sister Helen accompanied me in the trip from Gore to Waikaka. We parked not far from the old railway houses, outside the school, just down from two small grazing ponies, and walked down to the creek. There were trees here when we were children but they have recently been removed, pasture now running right up to the banks of the creek. The stream has a bed of stones. And along the stream sides, especially on the bends, there are areas of deposited stones.

The predominant stone is white quartz, sometimes stained brown, with a sprinkling of other types including quartzite. Surprisingly, we found a number of pieces of red jasper of varying shades, including some large rocks. 

The following are a number of the stones after being polished in 220 grit, the second stage of the five stage process of tumble polishing.

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A selection of individual jasper stones:

Three of the other stones collected:

I also came across, quite unexpectedly, a piece of petrified wood, and I also picked up another small whitish stone that could be some kind of petrified wood.

The two poles holding up the School sign are in old dredge buckets, remnants from a period at the start of the twentieth century when the area around Waikaka was busy with a number of gold dredges. 

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Since this trip, I have done some research into the history of gold mining at Waikaka. Later posts in this Blog will outline this history and the role of gold dredging around Waikaka and on “The Mains”.

“You run from the river, when it long ran over you…”

I once wrote the following in an article for a Smallfarmers magazine. It was entitled “The Passions and Emotions of Smallfarming: Place, Experience and Meaning”:

I was brought up on a large sheep farm in Southland. It was called “The Mains”, a Scottish term for the farm headquarters. My country childhood involved expeditions to every part – sheds, stables, pasture, river, pond, old railway line, shelter belts, pine tree plantations. I could be cowboy, farmer, hunter, explorer. I spent a lot of time fishing for trout in the river, building tree huts, hunting for rats and rabbits with Lassie, my fox terrier, riding horses, swimming in the river in summer, sledding down the snowy hillslopes in winter, often getting away from everything and enjoying being alone in my favourite grove of old gnarled pine trees or nestled down amongst the high grass not yet cut for hay. In autumn I gathered pine cones to sell to the “townies” to supplement my pocket money…I later bought Waikoha Smallfarm in the Waikato largely out of nostalgia for that long ago childhood – I had lived in cities for the previous three decades. There are many layers to the emotional meaning of my smallfarm, but one of the most basic involves a harkening back to my younger days… A smallfarm as a whole is emotionally-loaded to its owners. A smallfarm provides emotional comfort, independence and security. It enables a rural lifestyle characterised by peace and quiet, space, privacy, freedom and self-expression.

These photos (below) are of the Waikaka River running through “The Mains”, the farm I grew up on. I visited there on a stone-collection trip in April 2016. Gold mining dredges were active there in the late 19th century and again just recently – it is an area of inland alluvial gravel-beds. 

“Beside You” by Dave Dobbyn

Here’s to your garden, here’s to your kids
I heard you were in the neighbourhood
I’ve been a long time on the skids
And baby I’m beside you – you run from the river
When it long ran over you

This is for you standing up to a bone-chilling wind
This is for the failures you collected from my sin
And this is for your lonesome tears I never dried
This is for you hanging in in the hope that it never dies
And baby I’m beside you – you run from the river
When it long ran over you

This is for you waiting up though the call never came
For the milk of human kindnesses you collected from our dream
And this is for your lonesome tears I never dried
This is for you hanging in in the hope that it never died
And baby I’m beside you – you run from the river
When it long ran over you

And now I’m running here beside you
And now I’m running here beside you

This is for the traveller on a blinding desert road
Good fortune smile upon you and may love be your only load
And this is for the only one who could quell my burning rage
To anyone whose been a broken man and anyone seen better days

Baby I’m beside you
And now I’m running here beside you
And now I’m running here beside you