Coming to the numbers, Wikipedia suggests that gold mining uses about 25 kW·h of electricity per gram of gold produced. If I get the order of magnitude right, that corresponds to 25 GWh per tonne. Current annual production is about 3000 tonnes, so that gold mining uses about 75 TWh per year, compared to a widely cited estimate of 30Twh/year for Bitcoin. But the majority of gold is used for jewellery and industrial purposes, with only around 40 per cent being used for private investment (governments hold gold in reserves, but they have been net sellers for many years). Entirely coincidentally, 40 per cent of 75 is 30.So, the barbarous relic and its high-tech replacement use about the same amount of electricity every year. Gold is probably more widely used as a pseudo-currency than Bitcoin. On the other hand, gold mining has a lot of destructive effects in addition to the electricity used.So, at least arguably, gold and Bitcoin, considered as alternatives to the standard financial system, are about equally destructive in environmental terms.