Sark, Bailiwick of Guernseyi

Regional Level Types
Sark	Island
Bailiwick of Guernsey	Crown Dependency

The island of Sark consists of two parts, Greater Sark in the north and Little Sark in the south, that are connected by a narrow natural causeway.

Sark (French: Sercq; Sercquiais: Sèr or Cerq) is a part of the Channel Islands in the southwestern English Channel, off the coast of Normandy, France. It is a royal fief, which forms part of the Bailiwick of Guernsey, with its own set of laws based on Norman law and its own parliament. Sark (including the nearby island of Brecqhou) has an area of 2.10 square miles (5.44 km²).

Geology:
"The geology of Sark is given in Figure 5. The island consists of Pentevrian folded pelitic and hornblendic gneisses intruded by foliated granitic sheets, the latter forming Little Sark to the south and the extreme north of Great Sark (Sutton & Watson 1957).
The island has a number of mineral veins and the majority were explored between 1833 - 1845. These include the copper and silver lodes at Le Pot, copper-silver lodes at Port es Saies and a 5m wide chalcopyrite-calcite vein on the island of Brecqhou. However, the most important vein was Sark's Hope lead-silver lode on Little Sark (Mourant & Warren 1934, Laffoley 1985a).

The lodes at Le Pot were first discovered by John Hunt in 1833 (although Lukis claims to have collected material in 1817) and both were explored from 1834 - 1836 before being abandoned. The Le Pot Copper Lode was followed for more than 150m whilst the Le Pot Silver Lode, only 60cm wide, was explored for a much shorter distance, although it was said to carry good indications of quartz, galena and antimony-rich silver (Henwood 1871). Material from the Lukis Collection labelled 'Le Port (sic) Sark galena and ?silver' only showed galena, pyrite and altered pyrrhotite. Material from the copper lode (also from the Lukis Collection) consists of blue copper sulphides including chalcocite and djurleite and a little bornite.

At Port es Saies three parallel lodes, the largest of which was explored at two levels, were said to carry quartz, gossan, chalcopyrite and argentiferous pyrite (300 - 450ppm Ag). No ore was recovered (Henwood 1871). No material from Port es Saies has been seen but elsewhere on the island small veins carry some or all of the following assemblage: magnetite, haematite, pyrite, marcasite, pyrrhotite, galena, sphalerite, chalcopyrite and bornite.

In 1836 a chance find during a rabbit hunt led to the discovery of lead-silver ore, a find that was to become Sark's Hope Mine. By 1839 ore was being exported, approximately 250 Cornishmen had been imported (doubling the population), a small gauge railway and steam pumps installed and a rich vein of silver exploited. A silver tea and coffee service was on display in St Peter Port to encourage investment and day trips were organised. But leaner times were to come: as the vein narrowed, the ore became poorer and the mining depth increased. It has been estimated that the mine had a strike length of 600m, went to a depth of 200m and that £34,000 was invested for a £4,000 return from "25,000oz of fine silver and many tons of lead" (Laffoley 1985a). One of the main casualties of the mine was the Le Pelley family, the seigneurs of Sark, one of whom, Ernest Le Pelley, mortgaged the fiefdom for £4,000 to a Guernseyman, Jean Allaire, an ex-British privateer and freelance "French" pirate who owned the island of Jethou. In 1852 the mortgage was foreclosed and Allaire's daughter became seigneur (Gibbons 1975, Bell 1988).

Mining ceased in 1845. In addition to the geological reasons for failure, the running costs were too high. Fuel in terms of coal for the steam pumps had to be imported (the islands have no indigenous fuels) and the costs of shipping the ore for smelting, initially to Hull but later to Devon, also were too great.

The silver-lead mineralization occurred as a brecciated vein, trending 037o and between 0.5 and 3m wide, that cut foliated hornblende granite. An associated copper lode between 0.7 and 1.5m is composed of pyrite and thin stringers of chalcopyrite (Henwood 1871).

Contemporaneous accounts stressed the vertical and lateral zoning of the ore with lead-silver mineralization to the southwest of the lode, passing into silver without lead to the northeast, and that oxidized secondary ores overlay primary sulphides and sulphosalts (Henwood 1871). The mineralization has been described by Bishop et al (1977) and Ixer & Stanley (1983).

The primary ore (collected from the tips on the north-eastern end of the lode) is composed of pyrite and quartz in a galena or, locally, chalcopyrite and tetrahedrite cement with subordinate amounts of marcasite and sphalerite. Minor amounts of bravoite, acanthite and pyrrhotite occur. Gangue phases are haematitic, quartz, calcite and illite.

Silver is present in the antimony sulphosalts, polybasite, pyrargyrite and tetrahedrite (up to 23 wt % Ag) and to a lesser extent as the arsenic sulphosalts, pearceite and tennantite (up to 20wt % Ag).

Other than at Sark's Hope Mine the mineralization as described and seen on Sark is like that of the other islands. Sark's Hope Mine differs, however, both in scale and in metal and mineral assemblage and is closer in style to some of the economic lead-zinc-silver deposits of mainland France than to the poor mineral occurrences of the Channel Islands."
(http://www.rosiehardman.co.uk/taxev.htm)

Fossils

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Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Sark
Wikidata ID:	Q3405693
GeoNames ID:	3042282

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