London — Ray Ferguson has probably handled and admired more emeralds, sapphires, and rubies than any European monarch or Indian maharajah. For a quarter of a century he has been mining gems in countries as diverse as Afghanistan, Colombia, Brazil, Zambia, and South Africa.
Yet if he were to single out one country that most conjures up an Aladdin's cave of precious stones, it would be the East African nation of Tanzania.
''Tanzania has always interested me tremendously because it is a country with immense untapped mineral resources,'' he says in an interview in his elegant London townhouse.
Encouraged by the mining possibilities, Mr. Ferguson had a team prospecting in Tanzania prior to the country's independence in 1961.
''It was just phenomenally rich,'' he says. ''The potential there is absolutely fantastic. There is more potential there in the minerals and precious stone sphere than nearly any other country, including Brazil.''
After exhaustive negotiations with Tanzanian officials and three visits in 1981 to inspect the mines of Merelani (which are rich in tanzanite, a fragile precious stone made the house stone of Tiffany's of New York); Umba (sapphires and rubies); Longido (rubies); and Manyara (emeralds and alexandrite, a two-tone stone that apparently originated in the Soviet Union), Mr. Ferguson was hoping his mining company, African Minerals Corporation - Bermuda, could finally begin mining operations at least at the tanzanite mine last year.
But at 5 p.m. on June 23, 1983, after his plane touched down at Dar es Salaam airport, Ferguson was taken into custody and questioned.
Although he had made numerous visits to Tanzania before, is personally well known to several top Tanzanian Cabinet ministers, and had official statements confirming his mining applications, neither police nor immigration officials at the airport professed any knowledge of his mining venture.
Ferguson's British passport was stamped, then canceled, and he was thrown into jail.
After harrowing experiences in several Tanzanian prisons in which he contracted malaria, pleurisy, and pneumonia and lost some 70 pounds because of the ''shocking food,'' he was finally served with a Prohibited Immigrant Notice on Aug. 27, 1983.
That was the day he was let out of Keko Remand Prison in Dar es Salaam and sent to make his own way out of the country.
Mr. Ferguson might have been left to languish in Tanzanian jails longer had intense diplomatic pressure not been applied in both London and Washington to secure his release.
The miner now is fighting to have the Prohibited Immigrant Notice rescinded so that he and his partners can be allowed back into the country. He claims he had invested $700,000 ''out of my own back pocket'' in the country.
But does he want to return, after what he has been through?
''That depends on what conditions,'' he replies.
For three to four weeks during his confinement, his daughter Kim and son-in-law - who were stationed temporarily in Tanzania to carry out the project - had no knowledge of his whereabouts. This may be because Ferguson was shifted among three places of detention after he was taken at the airport.
The detention, after leaving the airport, began at the Criminal Investigation Department headquarters on the harbor front.
''I was stripped down to my underpants and undervest and thrown into the cells, which were almost half under water,'' Ferguson says. ''Fortunately there were some Kenyan Africans (in the jail). They pulled me into the first cell, where there was the only light available in the whole corridor and where there were fewer mosquitoes because of the light. They befriended me.''
A week later, a dirty sheet was thrown over Ferguson's head. He was then driven by jeep to another building about three quarters of an hour's ride away.
He does not know the precise location of this building, but believes it was close to an airport because he could hear planes landing and taking off.
Here, Ferguson was kept in solitary confinement in a locked room. Thick plastic was nailed over the windows and an electric light burned constantly, he says.
''I was there for eight to nine days, seeing nobody but my two guards and the two officers. . . . I think they came about three times to question me.
''At no stage did they subject me to any torture or to anything physical, although on occasion they did resort to shouting to me and telling me that I was lying and that I was a South African spy, which was the allegation.
''Actually they put it more gently. They said they were investigating to see if my 'South African background' was suspect.''
A Tanzanian spokesman interviewed by this newspaper concedes that Ferguson's background may have been a factor in his detention. Ferguson is a British citizen, but he was born in South Africa. For a time he lived in Bermuda.
Tanzanian authorities knew of this background, however, since they had previously approached De Beers Mining Corporation in South Africa for a reference on Mr. Ferguson, who mined emeralds there from 1959 to 1973.
Ferguson's arrest at Dar es Salaam last June was the sequel to a journey that had originated in South Africa. Before flying into Tanzania, he had been in Natal Province in South Africa, visiting his elderly mother in an old age home.
Tanzania, an outspoken critic of South Africa's apartheid policy, has no diplomatic relations with South Africa. As a prominent southern African ''front-line'' state, Tanzania has in the past claimed that South Africa is trying to undermine governments in the region.
Tanzania is in a calamitous economic situation. The island of Zanzibar, which is united politically to Tanzania, in particular is reported to be simmering with unrest.
In January 1983, some 30 Tanzanians, mainly middle-ranking Army officers, top businessmen, and a personal adviser to President Julius Nyerere, were charged with plotting to assassinate Nyerere.
According to informed sources, several unsuccessful attempts have been made to unseat President Nyerere, the doyen of African heads of state.
Although respected and internationally honored in the past for humanitarian acts and having raised social standards in his country, Nyerere and his radical socialism are also blamed for Tanzania's precipitous economic decline.
Two of the ringleaders of that January 1983 coup - Pius Lugangira, a businessman, and Hatti Maghee, a former Tanzanian Airways pilot - escaped from Keko, a maximum security prison, with the help of a warder who had been bribed just two weeks before Ferguson was transferred to this prison.
''But I met with everyone else in the party,'' he says. He also adds that there was no chance of escape since the prison was surrounded with troops. And even on the rooftops, there were soldiers armed with submachine guns.
''My cell was right next to the section of the prison where they used to search prisoners coming in for the odd court session and the torture area, where they treated prisoners very badly.
As in his previous detentions, the miner insisted he himself was never physically abused.
Ferguson says there were as many as 10,000 prisoners at Keko Remand Prison. Despite its name, ''There were inmates who had been there up to 15 years without a trial,'' he says.
The most distinguished inmate in Keko Remand is one of Tanzania's foremost diplomats, Christopher Ngaiza. Mr. Ngaiza - a former Tanzanian ambassador to the United Nations, London, and Washington - is suspect in the eyes of the current Tanzanian authorities because he is the uncle of Mr. Lugangira, one of the two alleged plotters who escaped from Keko.
Ferguson suspects that many of his fellow detainees, whom he described as the elite of Tanzania - top military men, engineers, and businessmen - were arrested for political reasons.
In the case of influential prisoners, the arrests appear to have been done at considerable economic and social cost and dislocation to the country.
He cited the example of his close cell friend, Abdul Haji, the personal representative in Tanzania of the Aga Khan, spiritual leader of the world's small, but commercially powerful, Ismaelite community.
As the Aga Khan's representative, Mr. Haji is chairman of the Aga Khan's bank and of numerous light industries in Tanzania. The Aga Khan's enterprises are considered to be part of the backbone of Tanzanian industry.
In retribution for what was done to Mr. Haji - he has been detained three years without charges - the Aga Khan has not invested further funds in Tanzania. A hospital slated for the town of Dodoma, for example, will now go to Pakistan.
The Medical Institute at the University of Dar es Salaam is floundering because of the arrest of another inmate - Medical Institute dean Muali ''Doc'' Mwaluko. The professor was arrested on charges of stockpiling a small crate of essential medical supplies.
Tanzania's export bean market has collapsed because of the arrest of yet another man, a prominent German farmer by the name of Steyn.
Ferguson, whose name is a household world to famous mining houses, maintains that if he had not been arrested and subsequently obliged to leave Tanzania after two months of imprisonment, his company could have materially assisted the impoverished country.
Feasibility studies had showed that in the first seven years of the Merelani mine, Tanzania could have reaped $22 million in revenues.
Ferguson was returning to Dar es Salaam in the hope of finally clinching the deal when he was arrested.
On his eventual return to London, Ferguson held discussions with both the British Foreign Office and the Nigerian high commissioner (ambassador), Anthony Nyakyi, ''on the basis that the case against me would be clarified and if all went well they would rescind my PI (Prohibited Immigrant) notice and allow me to go back.''
''I have waited many months until now waiting for this to be done. I have not been giving stories to anyone hoping this would be done, but I have heard nothing and have been informed from friends in Tanzania that I was not likely to hear anything either.''
Several attempts to reach High Commissioner Nyakyi to determine if Ferguson's status was under review have been unsuccessful. He was reported to be out of the office.
This reporter was then referred to the Tanzanian Embassy in Washington because his calls, which were initiated in Europe, later were placed from Boston.
Tanzanian Ambassador Benjamin Mkapa remembered meeting with Ferguson's relatives, who had taken up the case with other interested parties in Washington.
As a result of interventions by Ambassador Mkapa, Ferguson's daughter was able to visit him in prison and he was later released.
But Ambassador Mkapa indicated that it was not his prerogative to decide whether the order against Ferguson should be rescinded.