Ashanti Gold Mine

stamp mills gold mine crusher

stamp mills gold mine crusher

ABSTRACT: In 1990 a set of stamp mills dating from the early years of the operations was rescued from Sansu at the southern end of the Ashanti Mine open pit operation, thereby prompting the research on which this paper is based. The history, usage and construction of stamp mills is briefly reviewed. The early history of the Ashanti Mine in Ghana is then discussed with special reference to the numerous stamp mills that were erected and used between 1890 and 1916. As the operation expanded a large range of stamp mills was constructed with variable degrees of success. Progress was also hampered by the fact that until the arrival of the railway in 1903, all machinery had to be brought from the coast as head loads by local carriers. The operations were rationalised in 1905, as new technology was slowly introduced, with stamp milling finally ceasing in 1916. Parts of the stamp mills which were rescued are briefly described, and the known information about all the individual mills is discussed.

INTRODUCTION

Ashanti Goldfields Corporation (Ghana) Ltd. in Ghana (formerly the Gold Coast), has been working some of the richest gold deposits in the world since 1897, and it is testimony to the richness of these deposits, that after over ninety years continuous production, Ashanti was in 1988 the sixth largest gold mine in the free world. The mine was described by Cappendell (1987), and the recent expansion programme funded by a consortium headed by the International Finance Corporation, which will ultimately increase production to one million ounces per year, is described by Jonah and Cox (1991).

At present the surface and underground workings are concentrated in the area between Obuasi in the north, and Sansu in the south. Underground production is from high grade quartz reefs hosted in a major shear system with associated lower grade sulphide selvages. The country rock consists of Lower Proterozoic metasediments and igneous rocks with the shear system controlled by the contact between the two rock types. From the surface, open pits work lower grade oxidised equivalents of the underground ore.

This paper arose as a result of the rescue of the early Sansu Mine stamp mills during 1990, which were threatened with being engulfed by the expansion of the neighbouring Sansu open pit mine. Research into the history of the stamps revealed that far more information had survived than had been believed, which prompted this paper.

It is not the intention here to relate the history of how Ashanti came into being and against huge odds survived and grew to become the great mine it is today. The full history will be related elsewhere and is partially documented by Eaton Turner (1947). The present aim is to firstly examine the history of the stamp mills at Ashanti and the part they played in the early years of the mine, and secondly to describe the industrial archaeology of the stamp mills today.

STAMP MILLS – AN INTRODUCTION

The evolution of stamp mills will also not be considered here, but a brief description will help in understanding how stamp milling evolved at A.G.C..

A stamp mill can be thought of as being like a domestic pestle and mortar, with the ore being crushed between the pestle and mortar. A stamp mill is very similar: It consists of a large box or ‘mortar box’ with a means of introducing ore and water at one side. The ore is crushed between the ‘head* (the pestle) and the ‘die* (the mortar), both of which are enclosed within the mortar box, and allowed to discharge -normally through wire screens – as a finely ground product. The heads (or ‘shoes’) are attached to the bottom end of vertical rods or ‘stems’. The stems are lifted by the action of cams on ‘tappets’ or ‘collars* attached to the top end of the stems, and on being allowed to drop thereby crush the ore between the heads and the replaceable dies. The crushed material, as a muddy pulp, laps up against the screens and the finer material passes through, the coarser being retained for further crushing.

Stamp mills are first thought to have been applied to gold mining at the beginning of the sixteenth century, and over the years they became very sophisticated affairs. The Californian pattern, of which all the surviving stamp mills at Ashanti are examples, had a cam arrangement whereby the lifting action on the tappet also rotated the stem, thus evening out the wear on the bead* The dies could likewise be periodically rotated to even out wear. Screens on the mortar box discharge were introduced in the Hartz mountains in the eighteenth century, so as to ensure that an even product resulted. It has been known for centuries that if finely divided gold is mixed with mercury, then an amalgam is formed. The gold can be recovered from this amalgam by distilling off the mercury, which leaves a residue of spongy gold. Recovery of gold by lining the mortars with mercury-coated copper plates was first recorded in California in 1850. This was known as ‘inside amalgamation1. ‘Outside amalgamation9 was where the crushed ore was passed over similar plates outside the mortar boxes.

Stamps are generally referred to by weight, the weight given referring to the weight of the head, stem and tappet assembly, and this convention has been followed here. A ‘battery’ was a set of heads and a mortar (normally three or five), and conventionally the size of a stamp mill was expressed as ‘heads of stamps’, but the term ‘battery* was also used. Three head mills were normally used for prospecting, and five head mills were preferred for production as the order in which the stems dropped minimised vibration.

THE EARLY YEARS

Gold has been mined for many centuries on the Gold Coast, and the industrial archaeology of the pre-European native mining methods will be the subject of another publication. The first authentic record of trading in gold was by the Portuguese in 1471, and thereafter trading was to continue, with later the Dutch and the British, and finally the British alone after 1872, A string of forts along the coast bears witness to the many years of colonial rule and dispute (see Kesse, 1985).

A Frenchman, Marie Joseph Bonnat, who had at one time been a prisoner of the Ashantis, initiated the first modern gold mining in the southern part of the country at Tarkwa in 1878 (Rosenblum, 1972). British exploitation started in 1880 (T. Secretan, oral communication). It was not until 1890, however, that two enterprising Cape Coast merchants, Joseph Edward Biney and Joseph Ettrusion Ellis, crossed the Pra River into the Adansi state and negotiated the mining concessions at Obuasi (Rowe, 1991a). Ellis subsequently started work and sunk small shafts on the surface outcrop of the Obuasi Reef. Ore was crushed using three small hand powered three stamp mills and the mine was known as the ‘Ellis Mine* for the next seven years (Rowe, 1991a).

Biney was the West African agent of the London merchants of Smith & Cade, through whom he had ordered the stamp mills (T. J. Rowe, written communication). He sent quartz specimens to London, but these met with little interest until Edwin Arthur Cade joined the firm as a partner. He arranged to meet Biney and Ellis at Cape Coast and together they travelled to Obuasi in July 1895, and the concession was handed over to Cade on 16th August. In June 1897, after over a year of negotiations, the Ashanti Goldfields Corporation Limited (\A.G.C/) was formed.

Cade mounted his first expedition to work the concession towards the end of 1897, taking along with him John Daw as mine superintendent, fifteen artisans and forty tons of machinery. The task was very daunting. There was no harbour at Cape Coast so all personnel and equipment had to be landed through heavy surf. In the words of Thomas Madgwick, who was a mine engineer between 1899 and 1900, 4to get into the boat from the rolling ship and then go two or three miles alternately seeing the coast and the ship, with the final dash through the breakers, is something one never forgets’ (Madgwick, n.d.). The maximum load in a surf boat or canoe was 10 cwt.. Cade himself being delayed in Cape Coast, Daw went on ahead and the party reached Obuasi on Christmas Eve, 1897.

The challenges that faced Daw and his men must not be underestimated. At the time they mounted their expedition, since 1874 only one mining venture in the country out of many, the Wassau (Gold Coast) Mining Company, had met with any success (Rosenblum, 1972)* In addition the concession lay deep within Ashanti territory, outside the Gold Coast Colony. This could only be considered to be hostile territory, as the British and the Ashantis had clashed on a number of occasions during the previous decades (Lloyd, 1964). In the eyes of many the whole venture must have seemed as though it would be doomed to end in failure and was a foolhardy risk.

Work on erecting the stamp mills started in January, 1898, and within two months of arrival on site, in March 1898 a five-stamp mill of 380 lb. had been erected and tested at Obuasi. Shortly after that production commenced and by the end of June 262 tons of ore had been crushed, yielding gold worth £2,665 (Feldtmann, 1920). The first shipment of gold won from the property was made in July, 1898. During July the parts for a further five stamps of the same weight began to arrive on the mine, but the wet season hindered the work, often making the transport of the heavier loads difficult or even impossible (Daw, 1898a), and the problems of bringing equipment up to the mine from the coast dominate Daw’s reports until the arrival of the railway in 1903.

THE PROBLEMS OF TRANSPORTING MACHINERY TO THE MINE

The only way to bring equipment from Cape Coast to the mine, a distance of approximately 120 miles, was to headload it using local carriers. The road between Cape Coast and Kumasi was in bad repair, but the route between Fumsu and the mines, a distance of some 21V6 miles, was little more than a narrow path. At first great difficulty was experienced in getting carriers, and for the heavier loads of 90 to 175 lb it was necessary to pay up to £70 per ton, the average being £60. Later, with the clearing of a track between Fumsu and the mine, the difficulty virtually disappeared, and it even became possible to get a good part of the carrying done by contract through the local chiefs and headmen (Rowe, 1991a). The routes that were followed by these early pioneers can be traced in the names of local villages: *Brofoyedru* is a common name in the southern part of Ghana, and can be literally translated as ‘the white men are strong’.

An idea of the immense problems in getting materials up from the coast, and why the continual delays were so understandable can be judged from the following excerpt from Madgwick’s (n.d.) reminiscences:

‘ . .all stores were carried by native bearers including machinery which had to be sectionalism. Only in rare cases did especially heavy pieces require more than one man. The natives much preferred working singly although they travelled in parties and often had a system of working in stages, one man passing on to another until the load reached the mine. This was all right so long as the 4chit\ issued at the coast by our agent Mr. Biney, corresponded to the load accompanying it. Whilst I was at Obuasi the heaviest individual load to arrive was 204 lb. Heavy loads rarely touched the ground as that involved help in lifting them again; instead the carrier walked up to a tree having a fork capable of supporting one end of the load and then stuck his travelling pole under the other end and stepped out from beneath it. He reversed the process when he was ready to continue his journey. Such halting places were well known along the road as convenience of shape was a point of consideration when selecting loads. A favourite load was three 50 lb, boxes of dynamite or two for a woman – another being a 150 lb. shoe for the stamps in the mill.’

Another common load was rail for tramlines, which were initially made of wood. The lightest gauge available was 17 lb per yard, and two men would carry four twelve foot lengths, two on each shoulder. Interestingly, Covent Garden porters also used the method of propping up loads at head height. Who taught who? (T.J. Rowe, written communication) Maybe the method originated independently in Africa and England. Although die practise of propping up loads is rarely seen in Ghana today, during a recent drilling programme we filmed local workers moving heavy loads in the fashion described by Madgwick. It should also be noted that the women also carried their babies and food.

By August 1899, although problems were encountered during wet weather, sections weighing over 250 lb. had been successfully brought up from the coast in dry weather (Daw, 1899). The difficulties of bringing equipment from the coast were a constant source of problems, but the magnitude of the feat and the achievements should not be forgotten: In June 1900 Daw reported that the record for one man was 235 lb., that for a woman being 108 lb.. Since the start of operations 650 to 700 tons of machinery and stores had been brought up from the coast in loads of 70 to upwards of 400 lb. in weight. However, at times great difficulty was experienced in tracing missing sections ‘owing to the carriers dying en route or deserting their loads!’

Another problem was the landing of equipment at Cape Coast. At Anyinam (generally referred to as ‘Ayeinm’ in early references), for instance, work on the new 20 stamp mill started in 1899, but only ten stamps started work at the beginning of April, 1900. The delays were due to the fact that several pieces of machinery had fallen out of the slings whilst being landed at Cape Coast castle. In addition, a large number of sections had also been mislaid or broken in transit during the wet season (Daw, 1900). The rainy season extends from March to October, and rainfall in excess of 50 inches per annum is common.

The question of the mine being linked to the railway network had been discussed since at least 1900 (Daw, 1900). The railway from the coast finally reached Obuasi during the first half of 1903, and a daily passenger and goods service was initiated on 1st July, 1903 (Daw, 1903). The effect on the operation of the mine was immediate and far reaching as it ended the need to bring up all machinery and stores as head loads from the coast. Heavier loads could be imported, and more quickly too, as the import of the first cast mortar boxes to Obuasi for the second phase of the Sansu mill, early in 1903, bears witness.

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