Spot platinum fell for the fifth straight session, down 5 percent to a fresh 6-1/2-year low of $942.49 an ounce, due to oversupply, sluggish demand and weaker gold prices, which encouraged speculative selling.
"Illiquidity was important in the Asian overnight move, with Japan and other countries on holiday ... it was just a bit of a bear raid and there was nobody on the other side to mop up the selling," Societe Generale analyst Robin Bhar said.
"We have breached significant support levels, we know U.S. rate hikes are coming, there is no inflation and there is no catalyst to hold gold when other markets are doing better."
Gold fell more than 1 percent on Friday, pressured by increased bets on a Federal Reserve rate rise this year, which would increase the opportunity cost of holding the metal.
More than 3 million lots traded on a key contract on the Shanghai Gold Exchange, compared with fewer than 27,000 lots on Friday, Reuters data showed. Before Monday, the volume for July had averaged fewer than 30,000 lots.
Traders said it appeared that sellers had taken advantage of a low-liquidity environment, with Japanese markets shut for a public holiday, fueling speculative selling.
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"The break of the critical $1,130 support level now makes the technical picture look very weak," ANZ said. "Short-term supports sit at $1,085 and $1,050, while topside resistance at $1,130 looks pretty solid."
In wider markets, the dollar hit a three-month high against a basket of currencies, making dollar-priced gold more expensive for holders of other currencies.
China said on Friday its gold reserves were up 57 percent at 1,658 tonnes at the end of June from the last time it adjusted its reserve figures more than six years ago.
"This implies stockpiling of around 100 tons per year, which is dramatically lower than market expectations," Citigroup said in a note.
Palladium dropped as much as 3.4 percent to its lowest since October 2012 at $593 an ounce, before cutting some losses to trade down 1.4 percent at $605.25.
Spot silver, the least hit among precious metals in Monday's slide, was off 0.5 percent at $14.78 an ounce.