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Aviation vortices
The wings of airplanes in flight produce at least one pair of trailing vortices. These vortices are a major source of wake turbulence as they persist for a significant period of time after the airplane has passed. If the decay of trailing vortices were due solely to viscous effects in the core of each vortex, decay would be so slow that they would persist for hundreds of miles behind the airplane. In fact, these vortices only persist for tens of miles. The additional cause of the collapse of these vortices is large-scale instabilities such as Crow instability.

Sam Pearce
Samuel William Pearce (31 March 1848–1 January 1932) was a minerals prospector who is credited with discovery of multiple rich reefs of gold in a small region within Western Australia famously known as the Golden Mile. Since Pearce’s discoveries in 1893 the Golden Mile has been mined continuously and given rise to the twin towns of Kalgoorlie and Boulder.

Remaining gold within the Golden Mile is now mined from the giant Super Pit gold mine.

Early life
Pearce was born in England in 1848. At one-year of age his parents brought him to South Australia. The family settled in Kapunda where they ran a grocery store. Kapunda was a centre for gold mining and many Cornish miners lived in the region. Even though the young Pearce worked in his parents’ grocery store, he enjoyed talking to the miners and learning about their activities.

In 1867 he married Mary Williams, the daughter of a gold miner. In 1870 they settled on a farming property near Belalie. The property was eventually dotted with many holes as the results of Pearce’s attempts to find precious minerals. During this period of his life he is believed to have found copper, silver, lead, manganese, gold, asbestos and magnesite in the district.

In 1887 Pearce and his 14-year old son travelled to South Africa and went prospecting in the Transvaal and Zululand. They had some success and returned to Australia with some uncut diamonds.

While participating in a minor gold rush near Dashwoods Gully in the Mt Lofty Ranges of South Australia in the early 1890s, Pearce met William Brookman, an enthusiastic young man who had recently been at the centre of failure of a family business in Adelaide. Brookman was 10-years younger than Pearce but the two became friends and successfully worked a small mine they named the Great Boulder Alluvial Claim, possibly because to make progress they had to move heavy sandstone boulders.

(Glen Taggart, Mount Burr?)

Western Australia
When news arrived in South Australia in 1892 of exciting new gold discoveries in Coolgardie in Western Australia, Pearce and Brookman decided to pool their resources and try their hands on the west Australian goldfields. To gather adequate funds for their venture they successfully sought additional finance from William’s older brother George Brookman, a wealthy Adelaide businessman.

Pearce and Brookman sailed from Adelaide to Albany on 7 June 1893 on the maiden voyage of the P&O steamer Australia. Their passage cost them one third of their capital. After disembarking in Albany, they travelled by train to Perth and then by train to the railhead at York. In York they purchased 2 horses, a spring dray, mining equipment and provisions. They then set out for Coolgardie, a distance of approximately 285 mi. The dray was fully loaded with equipment and provisions so Pearce and Brookman walked alongside, reaching Coolgardie after 12 days. On arrival in Coolgardie on 28 June, Pearce and Brookman learnt of the discovery by Hannan, Flanagan and Shea of gold about 25 mi to the east where the town of Kalgoorlie now stands. Hannan had registered a claim 11 days earlier on 17 June. Rather than stopping in Coolgardie, Pearce and Brookman decided to walk the extra distance to the site of Hannan's new claim.

Discovery of the Golden Mile
Hannan's discovery of surface (alluvial) gold had precipitated a rush of prospectors to the area. Pearce and Brookman arrived only 3 weeks after Hannan's discovery but the number of prospectors already there was estimated to be about 3,000. All were searching for alluvial gold. Pearce regarded his objective as finding rich lodes of gold deep within the earth; rich lodes that would support a large-scale mining enterprise. It was his view that any rich lode of gold would be associated with ironstone, not with the quartz that was so attractive to the majority of prospectors already working in the area. Several years earlier, Government Geologist Edward Hardman had written that "the almost universal association of gold with iron oxides (ironstone) in auriferous deposits is remarkable."

Pearce went searching south of Hannan's find. About 3 mi south of the main camp he found "huge blows of iron". He marked the location and returned to the main camp. Before daybreak the next day Pearce and Brookman shifted their camp to the vicinity of these promising outcrops of ironstone. Pearce explored the area to the east of the new campsite. Less than an hour's walk from the new campsite he found the geological features he had been looking for. This was the famous Ivanhoe reef and would soon become the site of the Ivanhoe mine. The area would become the Golden Mile, soon considered the richest square mile on Earth.

Barely a month after Pearce and Brookman left Adelaide, Brookman walked back to Coolgardie to register the pair's claim. Then he continued west to Southern Cross to send telegraphs to the shareholders to convey the good news. He reported that Pearce believed the Ivanhoe mine would yield 3 to 4 ounces of gold to the ton of ore mined. This was an unusually high yield for a gold mine but ultimately it was achieved.

The Great Boulder Mine
While Brookman was absent walking to Coolgardie and Southern Cross and back, Pearce remained behind, working the Ivanhoe mine. On occasions he set out through the bush looking for further signs of the likely presence of rich reefs of gold. One evening he attempted to follow the ironstone formation that was proving the source of the gold in the Ivanhoe mine. In the twilight he found a large piece of diorite protruding out of the sand. In it, and despite the twilight, he could see traces of gold. He isolated a piece of the gold-bearing rock and took it back to his camp where he hid it. The next morning he returned to the site of his latest find and posted notice of his intention to claim an area of 24 acres (10 ha), the size of a mining lease. He took possession of the area on behalf of his company, the Coolgardie Gold Mining and Prospecting Company of Adelaide. That day, Brookman returned from Southern Cross and was astonished at Pearce's latest find. The two then completed the pegging of the area being claimed as a new mining lease. Pearce named it The Great Boulder in recognition of the name the pair gave their first successful gold mining venture in South Australia.

In August 1893 Brookman set out again, on foot, to Coolgardie to register the new claim. The Great Boulder lease was registered by the Warden in Coolgardie on 30 August, 1893. Brookman then continued to Southern Cross to send another telegraph to the shareholders in Adelaide: ''Have discovered an immense iron hill with very rich reefs running through, from one of which assays as high as 300 ounces to the ton have been taken. Have dollied 30 ounces of gold. Estimate the value at a quarter of a million.''

At the same time as development of the Great Boulder Mine and other rich mines nearby, a township sprang up 5 km to the south of Kalgoorlie. In 1896 this town was registered with the name of Boulder in recognition of one of the major mines employing the menfolk.

Norseman
At the end of 1893 Pearce returned to Adelaide to spend Christmas and the hottest summer months with his family. In early 1894 he sailed to Esperance in Western Australia and walked 180 km north to Dundas, opening up this route from the port to the Dundas area. His expertise was immediately rewarded by finding a site that, upon assaying, showed 100 ounces of gold to the ton. He also explored around Norseman, 200 km to the south of Boulder. Pearce found rich deposits that became the Leviathan mine, Lady Mary mine (named in honour of his wife), and the Daisy mine. He also travelled about 100 km to Lake Lefroy and, while there, discovered the site that was to become the Christmas mine.

Later life
Each new claim registered by Pearce and Brookman required substantial capital in order for a deep mine to be established and refining equipment to be purchased. Small established companies were restructured into larger companies, and new companies were floated. Chairman of several WA gold mining companies, Adelaide mining entrepreneur George Doolette, travelled to London to raise much of the capital required to exploit the rich reefs discovered by Pearce. Shareholders in Adelaide, London and elsewhere benefited greatly from these mining ventures but Pearce's share dwindled as the companies grew around him.

Biography of Sam Pearce

Elizabeth Warburton, 'Pearce, Samuel William (1848–1932)', Australian Dictionary of Biography, National Centre of Biography, Australian National University,

Biography of Sam Pearce