IN MINING, THEY CALL IT THE MOTHER LODE – AN ARTERY of precious minerals, hidden amid tons of bedrock, that can elude prospectors for years.

Along a single city block in London, a mother lode lies hidden.

The site is Charterhouse Street, a narrow ribbon of pavement tucked away from the four-lane clamor of High Holborn and Farringdon Road. According to guidebooks, the only landmark that distinguishes this street from any other in central London is a nearby bishop’s garden mentioned in Shakespeare’s ”Richard III.”

But there is something more here. Along both sides of this quiet lane stand the British headquarters of four corporations that, together, constitute the richest supply of gem diamonds on the planet, as well as the largest non-Communist supply of gold and platinum.

The corporations are De Beers Consolidated Mines Ltd., the Anglo American Corporation, Charter Consolidated and the Mineral and Resources Corporation (Minorco). The four pillars of this empire are situated like the corners of a cloister, De Beers and Minorco occupying one side of the block, Anglo American and Charter the other. During any business day, scores of employees, suspended some 30 feet above the pavement inside a glass-encased, split-level skywalk, shuttle like worker ants between the two office complexes.

Today is diamond day. It is an overcast winter afternoon -the kind peculiar to London, where the sun fades at 4 and the buildings, sidewalks and sky all resemble wet slate. I have a 3 o’clock appointment at the De Beers Central Selling Organization.

Nearly every major diamond-producing nation, including the Soviet Union, is represented by the C.S.O. It buys, stockpiles and then sells close to 85 percent of the world’s rough, gem-quality diamonds, doling them out at fixed prices at ”sights” held 10 times a year. De Beers refers to the C.S.O. as a ”single-source market”; critics describe it as one of the most disciplined and successful cartels in existence.

Inside, in the conference room, trays of unpolished gems are displayed under a harsh, white light, like bins of crushed ice at a fish market. This afternoon, 150 representatives from cutting factories have flown in from Antwerp, Bombay, New York and Tel Aviv. On arrival, each executive is handed a cardboard container the size of a shoebox. Inside are hundreds of diamonds filed in small envelopes according to size. The buyers retire to private booths to inspect their allotments. They can haggle over color and clarity, but the price is not negotiable.

Despite its location, the C.S.O. is not a British concern. It is South African. In fact, all four multinational companies clustered along Charterhouse Street can trace their founding to a single family: the Oppenheimers of Johannesburg.

HARRY OPPENHEIMER, 80 years of age, has dominated the South African economy for nearly half of this century. The C.S.O. is arguably the purest example of his monopolistic powers, but it is only part of a far-flung business empire known to his critics as ”the octopus.” With some 600 corporations, covering six continents and employing more than 800,000 workers, Oppenheimer’s diverse portfolio ranges from platinum to wood pulp, insurance to investment trusts, gold to daily newspapers. By some accounts, Oppenheimer’s collection of multinationals is bigger than ITT, Nissan or Siemens.

Oppenheimer presides over this empire from the modest helm of E. Oppenheimer & Son, a small, private company in Johannesburg that he runs with his son, Nicholas. On paper, the family’s only other holdings include 8.2 percent of Anglo American, 6.5 percent of Minorco and nothing of Charter and De Beers.

The structure of Oppenheimer’s empire is dizzyingly complex and nearly impenetrable to outsiders. He wields his power indirectly, through pyramided holding companies, interlocking shareholdings and a myriad of cross-directorships. As a result of this operating strategy, few people are aware that in the last two decades scores of businesses in the United States, Europe and Australia have been founded or purchased with Oppenheimer capital and are managed by Oppenheimer loyalists while maintaining no legal ties to South Africa.

Oppenheimer’s principal vehicle for diversification -and the most visible example of how his vast holdings operate – is Minorco (chart, page 42). Moved from Zambia to Bermuda in 1970, and later to Luxembourg, Minorco quickly became the chief overseas investor for the Oppenheimer clan. Roughly two-thirds of its shares are controlled by Anglo American and De Beers.

In 1981, with assets valued at about $2 billion, Minorco acquired interests in the Engelhard Corporation, the American mining and commodities trading conglomerate, as well as numerous other, smaller American mining concerns. (In the early 1980’s, Minorco entered the investment business via a stake in Salomon Brothers, the New York brokerage house, but Salomon bought back that interest in 1987.) Last fall, Minorco embarked on its most ambitious enterprise to date. On the morning of Sept. 21, it launched a hostile bid for a British firm, Consolidated Gold Fields Ltd., the world’s second-largest gold concern, whose assets include America’s richest gold mines.

With an offering price of $4.9 billion, it was the largest attempted takeover in British corporate history. But Gold Fields did not go quietly. The company had already been bruised by a stock raid in 1980 that had left Oppenheimer interests with nearly a third of its shares. This time, it was prepared. Marshaling attorneys, political lobbyists, investment analysts and detectives on both sides of the Atlantic, Gold Fields loosed a fusillade of charges against Minorco, ranging from allegations that a frenzy of insider trading in London and Johannesburg had preceded the bid, to speculation that Minorco’s corporate cousin, De Beers, had sold industrial diamonds to the Nazis in World War II. The evils of South African ownership became Gold Fields’ rallying cry.

From out of the fray, two issues of international concern emerged: cartels and apartheid.

GOVERNMENT OFFICIALS in Europe and the United States worried that the Gold Fields takeover could lead to a Johannesburg-based cartel in gold and strategic minerals modeled after Oppenheimer’s stranglehold on diamonds. Minorco’s acquisition of Gold Fields would leave Oppenheimer in control of one-third of the world’s non-Communist gold production. The takeover also would tighten South Africa’s grip on strategic minerals like titanium, platinum and zirconium – all essential to American defense and space industries.

Meanwhile, at Gold Fields’ American affiliates – among them, Newmont Mining, the largest United States producer of gold; ARC America, the principal domestic manufacturer of cement pipe, and Peabody Coal, the largest coal producer – executives worried about the apartheid issue. The stigma of being controlled from South Africa could, they claimed, cripple their ability to court government contracts, while leaving their companies vulnerable to boycotts.

To analysts familiar with the South African economy, Gold Fields’ counter-offensive was steeped in hypocrisy: the British firm has held a major stake in the South African gold industry for generations. But the strategy did succeed in buying Gold Fields some time. In October, Minorco’s tender was frozen – and subsequently it expired – while Britain’s Monopolies and Mergers Commission weighed the question of whether the bid would harm British consumers by restricting competition in metals markets. Gold Fields argued, among other points, that Minorco’s South African ties would hurt business; Minorco countered that it already was conducting business in Britain, the United States and elsewhere ”without inhibition.”

The review subjected Oppenheimer’s empire to public scrutiny of a sort it had rarely experienced. The Financial Times and other British newspapers carried front-page stories about Oppenheimer’s quest to conquer a historic archrival. As an outgrowth of Gold Fields’ countercharges, Britain’s Office of Fair Trading began a preliminary investigation of the De Beers diamond cartel – the first by any European authority.

In early February, the commission ruled that the takeover would not inhibit competition, clearing the way for a new bid. It came on Feb. 20, sweetened to $5.65 billion -which Gold Fields rejected. Minorco also announced that Oppenheimer and several associates will resign from its board of directors. A spokesman described the move as evidence of Minorco’s emergence as an independent corporate entity. Critics claim it is simply a smokescreen to allay concerns about South African control of the company.

In the United States, both sides await a Federal Court of Appeals ruling on an injunction that is blocking the takeover on this side of the Atlantic. A decision is expected shortly.

In making its ruling, Britain’s Monopolies and Mergers Commission took care to note that it had evaluated antitrust concerns, not political ones. Similarly, the United States court case involves an antitrust complaint, this one brought by Newmont Mining.

But the broader implications of the takeover are being felt on Capitol Hill, where the Minorco-Gold Fields battle has reshaped the debate over the role sanctions should play in United States policy toward South Africa.

For South Africa’s industrial elite, anxious that civil unrest could lead to the nationalization or destruction of their properties, expansion overseas offers long-term security. By diversifying through offshore holding companies and buying up interests in Western concerns, businessmen like Oppenheimer have evaded sanctions. Now, politicians and anti-apartheid activists who have long felt that economic pressure is the surest way to squeeze reforms from Pretoria are considering whether sanctions limited to companies that do business inside South Africa can be effective.

In addition to the Anti-Apartheid Act of 1988, which is to be voted on this session, Congress has before it a proposal to prohibit South African investors from purchasing more than 5 percent of an American company. Other proposals include calls to limit United States bank loans to businesses controlled from South Africa.

But can governments cauterize the flow of rand invested outside South Africa without endangering the jobs of thousands of American and European workers already employed by Johannesburg-based conglomerates? In the United States alone, Oppenheimer-controlled companies now employ more than 10,000 American laborers. If the takeover goes forward, that number will more than double.

The American Aggregates Corporation, a wholly owned subsidiary of Gold Fields based in Greenville, Ohio, is one potential victim. If the takeover goes through, hundreds of Ohio workers could find their jobs jeopardized by sanctions and loan restrictions included in proposed legislation.

”We’re beginning to appreciate that the fight against apartheid is not confined to South Africa,” says Pari Sabety, executive assistant for economic development policy to Ohio’s Gov. Richard F. Celeste. ”Deals made in Johannesburg, Luxembourg or London have a direct impact on a small town like Greenville.”

OPPENHEIMER’S first attempt to seize control of Gold Fields came on a February morning in 1980, in what executives on both sides refer to as ”the dawn raid.” For about three months preceding the raid, an investigation by Britain’s Department of Trade and Industry later found, De Beers secretly channeled up to 59 million rand – roughly $147 million – to six Oppenheimer-affiliated companies, instructing them to buy Gold Fields shares on command. This coordinated strategy was used to avoid violating Britain’s Companies Act, which requires any purchase of more than 5 percent in a company to be declared.

At 8:30 A.M. on Tuesday, Feb. 12, Anglo American’s London broker, Rowe & Pitman, was notified to begin the buying blitz. With 30 Rowe & Pitman staffers dialing their telephones simultaneously, Oppenheimer’s six-company consortium grabbed 16.5 million Gold Fields shares -close to 15 percent of the company – in less than an hour.

Standing between Oppenheimer and total control of Gold Fields were British regulations requiring a bidder controlling 30 percent or more of a company to make a formal tender offer. Such a move would not only be costly, but would attract precisely the sort of attention Oppenheimer sought to avoid. Instead, Anglo American and De Beers held at just under 30 percent, a stake they eventually transferred to Minorco. In the months that followed the raid, D.T.I. investigators announced that, through De Beers, Oppenheimer had ”formulated [ a ] scheme with the express intention of avoiding the disclosure provisions of the Companies Acts.”

In 1985, trade officials stitched shut the money-funneling loopholes that De Beers had managed to wriggle through. But the dawn raid had left Gold Fields with what one of its executives has since described as ”a predator in our pantry.”

Since then, Gold Fields has found itself reluctantly fused to a corporate structure that manages companies as if they were family. Anglo American and De Beers, the dominant members of the Oppenheimer clan, control more than one-third of each other’s shares, while sharing 60 percent of Minorco. Minorco, in turn, controls 36 percent of Charter Consolidated.

Other links run deeper than the balance sheet. Minorco currently shares four directors with De Beers, and six with Anglo American. Harry’s cousin, Sir Philip Oppenheimer, is on the board of De Beers; Harry’s son, Nicholas, holds a seat on the board of De Beers and is deputy chairman of Anglo American. Roger Phillimore, Minorco’s group commercial director, is Harry Oppenheimer’s godson. Gavin Relly, chairman of Anglo American; Julian Ogilvie Thompson, chairman of De Beers, and Hank Slack, director of Minorco’s American division, have all served as Oppenheimer’s personal assistants. Slack is also Oppenheimer’s son-in-law.

Although semi-retired, Harry Oppenheimer is still the most active steward of his family’s business interests abroad.

”The reason he is still so influential,” explains Slack, ”is that Mr. Oppenheimer is like a good father. He is extremely intelligent, tolerant and patient. His people enjoy working for him and he takes good care of them.”

In recent months, Oppenheimer has practiced a kind of corporate shuttle diplomacy, traveling between South Africa, Europe and Asia, conferring with his directors on strategy and issuing statements to the press on their behalf. Last fall, with Minorco’s bid for Gold Fields foundering, he was back in London laying out the merits of the offer in an exclusive interview with The Financial Times. ”I find it insufferable to be attacked on grounds of South African connections,” he was quoted as saying, ”particularly by a group which has been very active in South Africa and which has certainly not been in the forefront of opposition to the apartheid policy.”

According to a declaration that Rudolph Agnew, Gold Fields’ chairman, gave to the Monopolies and Mergers Commission, both De Beers and Minorco have attempted to coax Gold Fields and its major American affiliate, Newmont Mining, into the family fold. Agnew said he was privy to a series of conversations with Julian Ogilvie Thompson in which the De Beers chairman alluded to a veiled infrastructure of private holding companies sometimes used by Oppenheimer to pay his close associates – a largesse that is not disclosed to shareholders.

”He said, ‘We all get paid by Harry,’ ” Agnew recalled in an interview. ”There were vague suggestions that I could join the periphery of Harry’s extended family – an inner circle of very rich men.”

Agnew’s account complements information given to the Monopolies and Mergers Commission by anti-apartheid groups in Britain that links Oppenheimer to a tangle of private investment firms in the discreet banking environment of Switzerland or in tax havens such as Luxembourg, Liechtenstein, Liberia, Panama, Bermuda and the Netherlands Antilles. These holding companies, which collect South African capital and distribute it to Oppenheimer businesses throughout the world, include Central Holdings Ltd., a societe anonyme based in Luxembourg; the Vadep Holding Investment Company, a Swiss holding company, and Guyerzeller Bank, a private Swiss bank.

Julian Ogilvie Thompson at De Beers and several executives at Minorco deny that any covert trust exists. Minorco, however, revealed to the Monopolies and Mergers Commission that ”directors of the two companies [ Anglo American and De Beers ] and of Minorco are in part remunerated by a private Oppenheimer family company.”

AS MINORCO PREPARED to launch the hostile takeover, it faced several hurdles. It needed capital to finance the bid, it needed to defuse the South Africa issue and it needed to dispel its image as a Luxembourg holding company experienced in managing investment portfolios, not corporations. Last year, Minorco appointed as its chairman Sir Michael Edwardes, the scrappy and seasoned former head of the British Leyland Corporation, to lend an air of managerial competence.

Several banks in the United States and Europe were willing to accept the illusion that Minorco had no ties to South Africa. For Chemical Bank of New York, the only sticking point was the fact that the acquisition would include Gold Fields’ South African subsidiary. New York Comptroller’s Office guidelines prohibit loans to companies that do business in South Africa; the pension funds of government workers in New York, and possibly New Jersey, Michigan and California hang on this restriction, like a $100 million scimitar, to insure that banks comply. Incredibly, Chemical only demanded assurances that, after the takeover, Minorco would divest Gold Fields South Africa. (Several months later, Chemical conceded that its contract with Minorco violated the Comptroller’s guidelines – a tacit acknowledgment that Minorco is controlled from South Africa. Yet Chemical claims it is legally bound to its financing commitment with Minorco should the takeover proceed.) As soon as the bid was announced, analysts at Gold Fields produced statistics that allegedly demonstrated the impact the takeover would have on competition in the gold, platinum, titanium and zirconium markets.

The Gold Fields board retained a New York-based corporate detective firm, Kroll Associates. Kroll’s London staff, housed in the old MI5 building in Mayfair, trawled through a reservoir of financial reports, government documents, newspaper clippings and personal interviews.

In New York, Gold Fields’ Newmont Mining filed the antitrust suit against Minorco, Anglo American and De Beers.

In Washington, Gold Fields’ attorneys dispatched a 26-page letter to President Reagan, laying out their case. Correspondence followed from Senators Bob Dole, Pete Domenici and Daniel K. Inouye to Treasury Secretary Nicholas F. Brady, urging the Administration to review Minorco’s bid as a possible threat to national security under the Exon-Florio amendment to the 1988 Trade Bill.

The case drawn up by Gold Fields was simple: the takeover would leave South African industry with a sufficient share of gold and strategic minerals production to inflate their price and perhaps limit their availability.

In the case of gold, according to analysts at several New York investment banks, the massive stores kept by governments, scrap dealers and private investors would dilute any impact that a curb in current production might have.

When applied to strategic metals like titanium, however, Gold Fields’ claims seem more compelling. Gencor, the leading Western producer – mining 29 percent of the high-grade feedstock manufacturers require to make titanium metal – is owned and operated in South Africa. The second-largest source, Renison – extracting 25 percent of the West’s feedstock – is an Australian company in which Gold Fields owns a 48 percent interest. The Minorco takeover would place 54 percent of the world’s non-Soviet, high-grade titanium in South African hands.

Investment analysts familiar with precious metals warn that Gencor and Oppenheimer companies might then collude to control the world market for titanium, as they previously have done with platinum.

A South African cartel would leave American contractors with a painful choice: go hat in hand to South Africa or compete with other industrialized powers for a dramatically reduced pool of titanium feedstock.

NOT SURPRISINGLY, the most outspoken source of anti-Oppenheimer sentiment is Gold Fields’ chairman, Rudolph Agnew. He casts Oppenheimer as a Citizen Kane-caliber industrialist who lords over his empire from a South African Xanadu -”Brenthurst,” his sprawling estate outside Johannesburg. Agnew portrays himself, by contrast, as a modest company man.

”As much as any laborer in the mines, I am simply a paid hand,” Agnew explained in a recent interview at Gold Fields’ plush offices near St. James Square in London. ”Harry Oppenheimer’s Anglo American Group is manipulative and a self-professed believer in cartels. These companies are run by a small number of executives to suit the financial ambitions of the family. They are not driven by creativity or the desire to uncover new resources. It is a management style that, in mining circles, is known as ‘the dead hand of Anglo American.’ ”

Yet to those familiar with Gold Fields’ holdings, Agnew’s protestations about Minorco ring hollow. Gold Fields’ portfolio represents the largest British investment in South Africa, with 38 percent of Gold Fields South Africa and stakes in seven other mining concerns.

Moreover, accustomed to responding to strikes with force, Gold Fields billets one of the largest private armies in South Africa, complete with dogs, armored vehicles and its own patented rubber bullets. According to a documentary produced in 1986 by Granada Television, Gold Fields South Africa used videotaped propaganda to oppose the formation of unions for migrant workers. One video showed a well-dressed black man sitting behind a desk, dispensing advice as images of unemployment lines and malnourished women and children were projected in the background. ”Do nothing foolish,” the man cautioned, winking at the camera. ”Plenty of people want your job.”

For his part, Oppenheimer has managed to cement his place as the single most powerful businessman in South Africa while cultivating an international reputation as an unimpeachable opponent of apartheid. He served as an opposition member of the South African Parliament from 1948 to 1957. He has written widely denouncing the system of apartheid and lobbied other mining houses to support the establishment of unions. The executor of several charitable funds, he has helped finance schools and affordable housing for blacks.

Both Oppenheimer and his son declined to be interviewed for this story, but descriptions supplied by his business associates make the mining magnate sound as though he were an aging Oxford don. ”He has an enduring passion for his garden, loves the Romantic poets and collects first editions of Byron,” offers Roger Phillimore, Minorco’s group commercial director.

Specialists on the South African economy, however, say that Oppenheimer is deceptively modest about his holdings. ”South Africa Inc.,” an exhaustive chronicle of the family’s business empire published in 1987, calculated that the combined assets of all Oppenheimer-affiliated companies totaled 98.8 billion rand, or about $247 billion at current rates. The South African Government checked in at 98.1 billion rand, or $245 billion, for assets in state-run enterprises.

Anglo American, which accounts for more than 50 percent of the stocks traded on the Johannesburg stock exchange, permeates every conceivable corner of the South African marketplace: iron and steel production, engineering and heavy construction, automobiles and paper products, distilleries and slaughterhouses. (Before it was taken over by the state in 1970, the Anglo-affiliated African Explosives and Chemical Industries supplied ammunition to the South African Army and police force. In the chaos that followed the Soweto uprisings of June 1976, it was revealed that A.E.C.I. had manufactured the tear gas that police and mine guards used to silence demonstrators.) Despite Oppenheimer’s public stance on labor unions, when Anglo American was confronted with massive walkouts by the National Union of Mineworkers in 1987, it retaliated by dismissing 40,000 laborers.

Perhaps the crowning irony of the Oppenheimer-Gold Fields dispute is that both sides descend from the same imperial entrepreneur, Cecil Rhodes. Rhodes arrived in South Africa from England in 1870, at the age of 17, and by 1880, he was running a profitable diamond business. Several years after that, he crippled any possible competition by fusing two of the largest South African firms, De Beers and Kimberly. He also bought up scores of Boer farms, which split off in 1895 to become Gold Fields of South Africa. In London, Rhodes sold through the Diamond Syndicate, a consortium of diamond merchants who colluded to fix prices.

Harry’s father, Ernest, became chairman of De Beers in 1929. He revived the diamond syndicate after a rash of African discoveries between 1902 and 1919 deflated world diamond prices. The result was the Central Selling Organization that now stands on Charterhouse Street in London.

Ernest died in 1957, leaving Harry to usher the empire into a new, uncertain era, and to insure that it would weather political upheaval.

ONE WALL OF THE Anglo American-Charter Consolidated buildings in London bears a frieze carved in bas-relief. The lefthand panels depict Boer settlers on their Great Trek from Cape Colony in the 1830’s. The righthand panels portray Zulu warriors, whom the Boers had to subjugate before claiming the land.

The two halves of the frieze are divided, white from black, by a central section that displays the land and resources of Africa – then, as now, a wealth both sides fight to control. But the consequences of that fight now stretch far beyond the shores of South Africa to Britain and beyond.

In Washington, Representative Mickey Leland, a sponsor of the bill that would expand sanctions to cover South African interests in America, says lawmakers are just beginning to appreciate the implications of such investment.

”The package of sanctions and investment restrictions that Congress eventually adopts must reflect the sophistication of the economy we’re trying to isolate,” warns Leland, a Democrat of Texas.

Representative John R. Lewis, Democrat of Georgia, says: ”What many Americans fail to appreciate is that if we continue to allow South Africa to invest in U.S. corporations, we are effectively giving foreign aid to support the vicious system of apartheid.

”South Africa is attempting to short-circuit the U.S. political system,” adds Lewis, a longtime civil rights leader. ”Get constituents dependent on your investment, and you’ve built yourself a shield.”

Photos of Harry Oppenheimer (David Goldblatt) (pg. 32); Sir Michael Edwardes (David Goldblatt) (pg. 32); Rudolph Agnew (David Goldblatt) (pg. 32); process nation’s gold (Terry O’Neill/Sygma) (pg. 33); Chart of Oppenheimer corporate family interests (Source:The Guardian, The Independent, ”South Africa Inc” (pg. 42)