Introduction

For many years, the Mt Bischoff mine at Waratah in north west Tasmania, discovered by James "Philosopher" Smith in 1871, was one of the world's richest tin mines. From 1878, regular dividends were paid to shareholders, with several of them making fortunes. James Smith was not one of them.

Originally, the tin ore was treated by sluicing, then crushing as the ore grades reduced and the rock became harder, with 40 stampers, each of 1,000lbs capacity operating by 1914. It was so rich in places that it was simply shovelled into bags and shipped to the smelters located in Launceston.

From about 1910, the grade of ore began to decline, and with the price of tin falling heavily in 1914, the mine operated at a financial loss. From about 1929, the mine was worked on tribute, until the demand for tin rose in World War 2 when it was worked by the Commonwealth Government of Australia.

After 70 years of continuous production, the Mt Bischoff mine, the mountain of tin, finally closed in 1947. Since then, mining ventures have only been spasmodic. Exploratory drilling however, has indicated that there are still substantial reserves of ore, perhaps more than six million tonnes. If only the price of tin would rise.

For those interested in mineralogy, more than 100 different mineral species have been recorded from Mt Bischoff. These include aesthetic specimens of colourless, blue, green or purple fluorite, radiating topaz crystals, cassiterite nuggets of many kilograms in weight, as well as rare minerals such as ralstonite, sellaite, bavenite, and prosopite. The mineral pictured is a unique specimen of smoky quartz with purple fluorite and brown siderite, found a few years ago in dump material. The specimen measures 60mm. Although other specimens of fluorite were found, there was no other sign of smoky quartz.

Location and History

Mt Bischoff is located in north west Tasmania about 2km north of the township of Waratah, which in turn, is about 55km south west of Burnie. It is situated at the north east end of a strip of dominantly low grade silver-lead-zinc mineralisation, the most prominent of which is the Magnet mine (which was the subject of an article in the Australian Journal of Mineralogy Volume 1). Tin mineralisation occurs within the granitic mass that lies to the south of the Waratah-Corinna Road, and is associated with quartz porphyry dykes at Mt Bischoff and the nearby Mt Cleveland mine at Luina.

The summit of Mt Bischoff is around 900m above sea level, and rises about 250 metres above the surrounding plain. It is surrounded by impenetrable bush (as was the case with many west coast mines). The area is one of high rainfall and in winter can be covered in snow. However there are often water shortages in summer. In 1901, temperatures were recorded down to -9oC. This, coupled with an abundance of tiger snakes, can make collecting mineral specimens at Mt Bischoff hazardous to your health!

Mt Bischoff was named after the Van Diemans Land Company Chairman James Bischoff. The Van Diemans Land Company was granted enormous land rights in north west Tasmania in the 1800s.

It was the first major mineral resource developed in western Tasmania with a total production of around 62,000 tonnes of metallic tin concentrates. The discovery of tin was particularly important to the State as it provided the impetus for exploration of other areas of the west coast and the subsequent discovery of other mining areas such as Mt Lyell and Renison.

It is interesting to note that the Broken Hill outcrop was of interest to its discoverer, Charles Rasp, because he knew of the deposit at Mt Bischoff and thought that the Broken Hill deposit was a tin orebody.

Discovery

Tin was first found by James "Philosopher" Smith in 1871. Searching what he later named Tinstone Creek on the southern side of mountain, he located tin ore on the 4th December, 1871. He suspected that it was cassiterite that he had found, but was not able to examine it closely until the 6th when he reached a sunlit clearing.

Smith had been involved in prospecting for minerals for a number of years. He had joined the Victorian gold rush in 1851, and continued to prospect on his return to Tasmania two years later. This prospecting led him to discover gold in the Forth and Leven Rivers, and copper, iron and silver-lead at Penguin on the north coast. Prospecting was only a part time activity as Smith was also a farmer and timber gatherer.

Smith had previously come to an agreement with the Van Diemans Land Company to prospect for minerals on their land in return for 5% of net proceeds. His tin discovery at Mt Bischoff was only a few kilometres from the boundary of the company's Surrey Hills block.

The Early Years

The early years were difficult for the mine. There were many problems starting up due to the remote location, the rugged terrain, dense scrub, bad weather and lack of transport. Roads were often impassable in winter when rivers were in flood.

Early methods of transport included bullock teams and pack horses but in 1875 completion of the mine tramway replaced the worst section of track. The transport problem was relieved somewhat in 1878 when the Van Diemans Land Company constructed a wooden tramway. In 1884 the tramway was superseded by a railway to Burnie run by the Emu Bay Railway Company, famous for its links with other west coast mines.

Regular dividends were paid from 1878, and many shareholders made fortunes. Smith was not one of them. He had severed his connections with the Mt Bischoff Company in 1876 after a disagreement over the mine manager, HWF Kayser, and disposed of his shares before the first dividend was declared in 1878.

The mine was mainly worked as an alluvial mine for the first seven years. High grading was common. Sometimes ore was so rich it was simply shovelled into bags for shipment to the smelters built specifically for Mt Bischoff in Launceston. Tin from Mt Bischoff was to Launceston what gold was to Melbourne in the 1850s. Mining was by sluicing initially and at its peak, there were 32 sluices operating around the mountain. 1888 saw the first year of productive underground mining.

An early visitor to the mine was one George Ulrich of the Geological Survey of Victoria. Ulrich was invited to visit the mine in 1874 and collected specimens that are now housed in the Museum of Victoria. He was a significant contributor to the knowledge of Victoria's mineralogy and has a mineral named after him (ulrichite from Lake Boga).

Decline

Due to rich ore in the White and Brown faces running out, tin ore at lower grades, harder rock, and a greater pyrite content, the turn of the century also saw a turn in the fortunes of the mine.

To try to arrest the downturn, a new mill was built in 1914, with 40 stampers each of 1,000lbs capacity. A power station was also constructed with the turbines driven by what was known as the "Ringtail", a water race constructed to divert water from the head of the waterfall on the Waratah River.

By late 1920s, mine was on the downward slide with only some work allowed by tributors.

During the 2nd World War, the Commonwealth and State Governments took control of Mt Bischoff to provide tin for the war effort. This also coincided with the reopening of the Briseis Mine at Derby in Tasmania's northeast which had been closed because of cheaper tin from Malaysia. This Malaysian tin was off limits to Australia and its allies during the war.

The mine finally closed in 1947.

A Brief Revival

Between 1972 and 1976, a new mining venture was undertaken by the Ringarooma Tin Mining Company, designed to exploit alluvial tin at the northwest base of the mountain.

Mesh accepted tin up to 2" in diameter, so larger nuggets of cassiterite were rejected. Two large "nuggets" were reported (15lbs and 19lbs in weight) with one of these serving as a doorstop. Their whereabouts are currently unknown.

Future Prospects

Groves et al (1972) postulated that future prospects include reserves proved, probable and possible of dolomite-sulphide lode ore are about 1.3 million tonnes at 1% Sn. In addition, probable and possible reserves of quartz porphyry ore are about 3.4 million tonnes at 0.47% Sn. It is unlikely that mining will recommence while the price of tin remains at its current low levels.

Mineralogical Environments

Introduction

Precambrian quartzite, shale and minor dolomite have been intruded by a number of Devonian quartz-feldspar porphyry dykes, probably related to the nearby Mt Meredith granite.

Mineralisation is related to these dykes, and occurs as a replacement of the dolomite, greisenisation of the dykes, and as veins and fracture linings.

Tin mineralisation occurs in a radius of about 1km from the summit of Mt Bischoff, and minor silver-lead deposits occur towards the outer edge.

Over 100 mineral species have been reported, not all confirmed.

Dolomite Replacement Mineralisation

Dolomite replacement mineralogy is dominated by pyrrhotite with a carbonate (siderite or an Fe-magnesite) or one of a number of silicate minerals.

Highest tin grades were found within the quartz-pyrrhotite-topaz-fluorite assemblage (the most strongly altered dolomite replacement rocks), with relatively high grades in the talc assemblage.

Dolomite replacement mineralisation is found at the Greisen Face, where talc/pyrrhotite alteration occurs, and at the Slaughteryard Face, where quartz/pyrrhotite alteration and fluorite "nodules" occur.

Dyke Mineralisation

Greisenised dyke rocks are characterised by a hard, white, fine-grained groundmass of quartz and topaz, with orthoclase phenocrysts pseudomorphed by siderite (at the margins) or intergrowths of pyrrhotite, quartz, topaz, pyrite, fluorite and cassiterite.

One of the most prominent features of Mt Bischoff when viewed from the south is the Western Dyke, a greisenised porphyry with cassiterite disseminated in, and coatings on, joint surfaces. A theory as to the reason that these dykes are still there (ie: have not been mined out), is that the cassiterite occurred at the contacts, so the miners simply skimmed off the surface and left the "barren" core of the dyke.

Veins and Fracture Linings

Fissure lodes that cross cut sediments and dykes, and therefore a later phase of mineralisation, contain a complex assemblage of pyrite, pyrrhotite, galena, sphalerite, chalcopyrite, bismuthinite, As-Sb-Bi sulphosalts, wolframite, stannite, quartz, siderite, tourmaline, topaz, fluorite and cassiterite.

Major veins may average 700cm in width, with minor veins 2 to 4cm in width, the latter commonly consisting of quartz and cassiterite.

Post-Mining Mineralisation

Post mining minerals include mainly sulphates such as gypsum, melanterite, and copiapite.

Mineralogy

More than 100 different mineral species have been recorded from Mt Bischoff. Many of these are difficult, if not impossible, to find today, and may only exist in the literature, or as specimens in collections such as the Petterd collection in the Tasmanian Museum in Hobart. The Petterd collection includes examples of vivianite, stibnite and native copper. William Frederick Petterd was of course responsible for much of the early knowledge of mineralogy in Tasmania.

Mt Bischoff is particularly interesting because of the large amounts of magnesium and fluorine in the system producing rare minerals such as sellaite, chondrodite, norbergite, wagnerite and fluoborite. Other interesting minerals have formed through subsequent phases of activity, many through replacement.

Only minerals that can still be collected, or that are of particular importance, have been covered in detail below. Table 1 contains a list of all of the minerals that have been recorded or reported from Mt Bischoff. This list has been compiled from minerals recorded in available literature and supplemented by species collected by members of our Society.

Beryl - Pale to mid-blue opaque crystals of beryl up to 5cm in length have been recorded from Mt Bischoff. Some of these crystals exhibit colour zoning which can be seen on the flat terminations of the hexagonal prisms. Smaller crystals to about 1cm have recently been found near the Slaughteryard Face associated with an emerald green tourmaline.

Other beryllium minerals recorded from Mt Bischoff include bavenite, hambergite and phenakite.

Carbonates - It is difficult to visually identify many of the carbonates in hand specimens. Most specimens generally referred to as siderite may in actual fact be either an Mg-rich siderite or an Fe-magnesite (R. Bottrill pers comm). The general guide is that the lighter the colour of the specimen, the less iron content. However, many specimens are coated with iron oxides, making identification even more difficult.

Most siderite/magnesite is found as tabular hexagonal crystals and is common in the dolomite replacement bodies, often associated with fluorite. Crystals to 5cm across are known.

Cassiterite - Cassiterite was the most important tin mineral mined at Mt Bischoff (stannite and teallite are the other tin minerals recorded). It occurs in a number of environments, and was particularly abundant in the dolomite replacement bodies (especially the white and brown faces). Much of the cassiterite mined was eluvial or alluvial, released through weathering processes. In 1880, a 5 cwt solid nugget was recovered from the Slaughteryard Face. It is still possible to pick up "nuggets" (masses) of cassiterite up to 6cm from around the mountain. Many of these have bright euhedral crystals in cavities around the edges.

Bright red-brown or yellowish cassiterite crystals to 3mm can be found in a quartz matrix in the dyke rocks. Specimens are often difficult to extract intact due to the hardness of these rocks. The crystals tend to occur mainly as short prisms, often twinned. Cassiterite also occurred as encrustations on joint faces of sedimentary rocks adjacent to the dykes. Although it is difficult to find such examples in situ, as the edges of dykes have been skimmed off by the miners, diligent searching of tracks can provide samples.

Crystalline cassiterite generally occurs as equant crystals, where the length and width of crystals is roughly equal. One specimen discovered recently however, contains prismatic crystals to about 1mm where the length is about six times the width. It is difficult to determine whether this form was more abundant in earlier times.

Fluorite - Much of the fluorite collected in recent times has come from the Slaughteryard Face (a dolomite replacement body). The fluorite is found as cubes modified by octahedral (111) and to a lesser extent, dodecahedral (110) faces on a matrix of either magnesite or siderite. Most specimens are transparent lustrous crystals, either colourless or pale blue and range in size from a few millimetres to crystals 2.5cm across. Some thin veins of non-crystalline purple fluorite can also be found in this area. In addition, a single specimen of brown octahedral fluorite was found late last year. Associated minerals apart from the carbonates include beryl, tourmaline, pyrite and arsenopyrite.

In the late 1980s, part of the Happy Valley Face was worked for specimen material. Transparent colourless crystals of fluorite, almost always as cubes, sometimes elongated or flattened, occurred on Fe-magnesite. Associated minerals include quartz, pyrite and sphalerite. Very little fluorite can be found here today.

Green fluorite, sometimes with purple cores, has been found near the White Face dyke in recent years. Some cabinet sized specimens were extracted from here.

Some of the dumps have produced attractive specimens of dark purple fluorite over the last two years. All specimens recovered are comprised of individual crystals or aggregates of cubes modified to a greater extent than those from the Slaughteryard Face. These are thought to have occurred later in the paragenic sequence and have been protected in the mud of the dumps and are largely undamaged. Associated minerals include tourmaline, siderite, pyrite, marcasite and smoky quartz.

Fluorite can also be found in many other parts of the mine although today it is not as abundant as it has been in the past.

Other halide minerals include sellaite, which is abundant but not easy to recognise in hand specimens, the rare minerals prosopite, ralstonite and weberite, and halite and sylvite as inclusions.

Quartz - Abundant white and sometimes colourless hexagonal quartz prisms occur in the quartz-topaz porphyry dykes and in other areas such as the Happy Valley Face, occasionally as wheatsheaf aggregates.

Smoky quartz specimens are rare. One specimen is illustrated in the Catalogue of the Minerals of Tasmania (Plate 9). A second specimen (illustrated) was discovered late last year in a dump. It is a very aesthetic specimen comprising a white quartz (crystal) matrix with a group of doubly terminated smoky quartz crystals to 3.5cm in length, with a purple fluorite crystal (8mm) sitting behind the quartz terminations. Other purple fluorite and siderite crystals 2 to 4mm across are scattered on the matrix. Importantly, because the specimen was protected in mud in the dump, there is no damage.

Sulphates - A number of sulphates have been recorded from Mt Bischoff, occurring mainly as a result of post mining alteration of sulphides.

The most notable sulphate is melanterite which has been found as stalactites up to 30cm in length in adits and other protected areas. It is a very unstable mineral unless treated. Some stalactites were embedded in resin and have survived for many years.

Sulphides - Pyrite and pyrrhotite are ubiquitous, often found in varying stages of decomposition. The smell of sulphur is constant. You certainly know when you have been collecting at Mt Bischoff!

Pyrite can occur as groups of crystals, either as cubes to 2cm, rarely as pyritohedrons (pentagonal dodecahedrons), or in massive or disseminated form. Some pyrite collected does decompose, however if it is fresh and bright when collected, and it is stored away from moisture, it has a good chance of remaining intact.

Other sulphides found in crystalline form in recent times include arsenopyrite, marcasite and sphalerite.

Topaz - Quartz-topaz porphyry rocks contain a compact fine grained form of topaz known as pycnite, which is often found as pseudomorphs after feldspar. These rocks also contain radiating groups of transparent colourless crystals of topaz to 2mm.

A single crystal of yellowish topaz 6mm in size was found on a track in the lower workings of the mine, but it is possible that this may have been dropped by someone who had visited the Moina area as it very much resembles topaz from there.

Tourmalines - Tourmaline is common at Mt Bischoff. It generally occurs as blue or green thin tufted acicular crystals known as zeuxite.

As with carbonates, identification of specific species is impossible in the hand specimen. Many specimens have been analysed, with compositions ranging between dravite, a magnesian tourmaline, and schorl, an iron tourmaline. The lithium bearing tourmaline, elbaite has also been recorded. More investigative work needs to be carried out particularly on tourmalines from Mt Bischoff.

Summary

Mt Bischoff has been an important mine for the state of Tasmania, both for the economic benefits that have been derived from it, and from the diverse range of minerals that have been recorded. It is unfortunate that more specimens have not survived, as it is possible that many more species, perhaps even species new to science, could have been identified, from the unusual geological environments that occur there. This may yet happen if tin prices increase sufficiently to encourage new mining ventures.

There is still much to discover at Mt Bischoff........the Mountain of Tin.