The U.K.'s Financial Conduct Authority has also been looking at precious metals as part of a broader review of financial benchmarks. With an estimated 175 million ounces of gold, worth $215 billion at today's prices, changing hands daily on the over-the-counter market, London is the global center of gold trading. However, the FCA has not launched a formal investigation.
Some bankers believe BaFin has come under pressure to show it is willing to get tough on suspected market manipulation. It was widely seen to have been slow to respond to the concerns over possible manipulation in the forex market expressed by other regulators around the world earlier this year.
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Although the gold and silver fixings are, like Libor, set by small groups of banks, they contrast with the process for setting Libor in that they are based on trading activity rather than theoretical quotes.
Executives at major gold traders say their contact with the FCA on the subject has so far been largely limited to general questions. But the German regulator's probe into the foreign exchange market has moved beyond informal discussions with banks. BaFin is now asking for information in the form of emails and documents, said a person familiar with the situation.
The visit to Deutsche offices signals that BaFin now has greater concerns over the precious metals markets. Officials have asked to observe documents and processes related to precious metals trading as well as to interview bankers, the person said.
(Read more: Another week, another banking scandal)
BaFin confirmed that it had been looking into the possible manipulation of gold and silver prices, as well as foreign exchange benchmark rates, since the summer, but declined to comment on specific institutions. The regulator first confirmed it was conducting a probe into the gold and silver market in November.
Deutsche Bank declined to comment.