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KINGSGATE MINES Part 2

KINGSGATE MINERALS

(This is the second chapter of this booklet on Kingsgate Mines.) When I get time, I'll fix up all the chemical formulae.

The modern visitor to Kingsgate mines is probably hoping to find specimens of the minerals for which the place is justly famous. It is a classic locality for quartz crystals and molybdenite in particular but many more minerals are likely to be found on the dumps. More than 30 different minerals have been recorded at Kingsgate and the collector should have no difficulty finding specimens of at least 10 of these. They fall into two categories: ore minerals and rock-forming minerals and this is the order in which we shall examine them.

ORE MINERALS

Molybdenite, MoS2. This is the most obvious of the metallic minerals, easily recognised by its high metallic lustre and extreme softness. With a hardness of only 1 - 1.5, it will readily mark the fingers when handled. It is widespread on the mullock heaps, standing out against the white quartz in which it is frequently embedded. Careful searching will reveal specimens showing the hexagonal crystal shape and others displaying alteration to the yellow mineral ferrimolybdite. Specimens may also be found in which the crystals are found together as small rosettes.

Bismuth, Bi. A much more difficult mineral to find on the dumps, due to its greater value. Native bismuth is a brittle silver-white mineral with a distinctly pinkish tinge. It is relatively soft (2 - 2.5) and has a shiny silver-white streak, which is easily seen when specimens are rubbed against a piece of white quartz. The bismuth was usually found as masses between quartz crystals and occasionally as wires within white or transparent quartz.

Wolframite (variety ferberite), (Fe,Mn)WO4. A dense, brown to black mineral, wolframite is found scattered in pieces through the dumps. It has a prominent cleavage, making it easy to recognise because of the flat, lustrous surfaces created. It is comparatively scarce, but easy to recognise.

Cassiterite, SnO2 (tinstone). It was this mineral which the first prospectors were seeking at Kingsgate in 1872. It is scarce, being found in few of the pipes. Cassiterite is a hard, dense mineral, usually brown or black. Despite its colour, its streak is white unlike any of the other dark minerals likely to be found at Kingsgate.

Arsenopyrite, FeAsS (mispickel, arsenical pyrites). Another mineral with a metallic lustre, arsenopyrite is silver-white in colour with a black streak. It is much harder than bismuth and easily distinguished from it by its streak. It occurs plentifully in some pipes, usually as large masses in white reef quartz but is scarce in most.

Bismuthinite, Bi2S3. This is a rare mineral which was encountered in some pipes at Kingsgate in masses several kilograms in weight. It resembles native bismuth, with which it is often found, but is somewhat darker both in colour and streak.

Ferrimolybdite, Fe2(MoO4)3.8H2O (molybdite, molybdic ochre). Once thought to be molybdenum oxide, this canary yellow mineral is a common alteration product of molybdenite, with which it is often found. When found as crystals it occurs as tufts of acicular crystals up to 1 cm long.

Powellite, CaMoO4, with some tungsten substituting for molybdenum. Powellite forms by the alteration of molybdenite and is itself altered to ferrimolybdite. It is a rare mineral found in tetragonal crystals of bipyramidal habit of hardness 3.5 - 4. Its colour varies from yellow through greenish blue to nearly black.

Bismite, Bi2O3 (bismuth ochre). This is a somewhat earthy yellow to greyish green mineral found as an oxidation product of bismuth and bismuthinite, with which it is likely to be found. It occurs as fibrous masses in cavities in the quartz.

Bismutite, (BiO)2CO3. Another secondary bismuth mineral, this was one of the first bismuth minerals to be recognised at Kingsgate. It occurs as straw-yellow pseudomorphs after bismuthinite. It has sometimes been mistaken for gold by beginners, as it occasionally turns up in the prospector's dish. Unlike gold, particles of bismutite can easily be crushed to a powder.

Scorodite, FeAsO4.2H2O forms as an oxidation product of arsenopyrite. It is found as green botryoidal masses lining cavities in reef quartz formerly occupied by arsenopyrite.

Pyrrhotite, FeS, is occasionally found on the dumps. It has a metallic lustre, with a typically yellow-grey colour. Its streak is dark greyish black. The mineral is frequently slightly magnetic and oxidises on exposure to an iridescent surface.

Pyrite, FeS2, is occasionally found as pale brass-yellow cubes with an intense metallic lustre. Its streak is typically greenish black.

Chalcopyrite, CuFeS2, resembles pyrite but has a more golden colour. Surfaces are frequently tarnished and iridescent.

Galena, PbS, occurs from time to time as brilliant grey cubes, which cleave easily in a cubic fashion. Galena is denser than most minerals with a metallic lustre.

Galenobismutite, PbBi2S4, has been reported as greenish silver coloured masses up to 5cm across in molybdenite.

Ikunolite, Bi4(S,Se)3, is a rare mineral which has been reported at Kingsgate as plates and foliated masses with a prominent basal cleavage, lead-grey in colour.

Joseite, Bi3TeS, is another rare mineral reported from Kingsgate. It is a soft greyish mineral displaying one perfect cleavage.

Cosalite, Pb2Bi2S5, has been found from time to time as metallic lead-grey needle-like crystals.

Pyrargyrite, Ag3SbS3 (ruby silver), has been reported as soft, deep red prisms. The crystals display an adamantine lustre.

Gold, Au and Silver, Ag, have appeared in significant quantities in some chemical analyses of ore samples.

Brookite, gudmundite, sphalerite, chalcocite, covellite, marcasite, smythite, goethite, ilsemannite, tungstite and wulfenite have all become recorded at various times.

ROCK-FORMING MINERALS

Quartz (SiO2) is the overwhelmingly obvious mineral to be found at Kingsgate. The pipes consist essentially of quartz in which the ore minerals are embedded. The quartz varies a great deal from massive

to individual crystals up to 200 kg in weight, from milky to glass clear, smoky and rutilated. It is found as single crystals and as a variety of twin types. It is found alone and in company with crystals of the various ore minerals. Specimens of all types can still be found on the dumps and have made their way into collections all over Australia and beyond.

Rock Crystal. This is the term applied to the colourless variety of quartz which is much sought after for faceting, carving and just as specimens. It is not as simple as it might seem to find completely flawless material. Thousands of collectors have been to Kingsgate over the years to gather just such specimens. It will probably be necessary to search the more remote dumps and to dig deeply into them to locate the best material.

Smoky Quartz (cairngorm). Also much sought after, the colour of this variety ranges from a smoky yellow to brown or almost black. The colour is believed to be the result of partial decomposition of the quartz by exposure to radiation

from radioactive minerals. The presence of aluminium substituting for silicon atoms in the crystal lattice seems also to be essential. Smoky quartz can sometimes be decolorised by heat, the effect becoming noticeable above 225o and rapid above 450o. Some of the colour can be retained in a deeply coloured specimen by stopping the process before it is complete.

Citrine is the yellow to orange variety of quartz. Its colour appears to be due to the presence of small amounts of colloidal hydrated iron (111) oxide. Good specimens are not easy to find at Kingsgate, but some types of smoky quartz, evidently containing the necessary impurity, will turn into citrine when heated.

Amethyst, the much admired violet variety of quartz, is even scarcer at Kingsgate than citrine, which it much resembles chemically. The colour is due to the presence of iron (111) possibly substituting for silicon in the lattice. Strong heat will convert amethyst into an orange citrine.

Quartz with Inclusions. The following have been reported from Kingsgate: rutilated quartz (grass stone) contains fine needles of rutile (TiO2) penetrating the quartz. It has occasionally been found at Kingsgate. Arsenopyrite, bismuth, bismuthinite and molybdenite are fairly frequently found.

Calcite (CaCO3) occurs in white cleavable masses in some pipes.

Muscovite mica, as the variety sericite, is plentiful in the pipes, where it has been produced by the alteration of the original felspar. It can be recognised by its silky lustre, softness and lack of visible crystals.

Topaz and garnet (variety unspecified) have been reported from the dumps. Finding these would have to be regarded as a bonus.