Gold deliveries to central bank unit Fidelity Printers and Refiners, which buys all the country's gold, declined to 6.5 tonnes from 7.3 tonnes during the January-March quarter.
Sibanye Gold reiterated that its increased offer for Lonmin is final, but kept its option open to sweeten the deal for the platinum producer should a rival bid emerge.
A plan to build Zimbabwe’s biggest platinum mine at a cost of about $4 billion is floundering because a military stake in the project has deterred potential backers.
Higher prices for a basket of Lonmin's metals and a weaker South African rand helped the London-listed miner to an annual pre-tax profit in 2018, its first since 2013.
Specialist materials firm Johnson Matthey forecast a 127,000-ounce platinum shortfall this year, after surpluses of 372,000 and 44,000 ounces in 2018 and 2017 respectively.