Shares of London BTC Company Ltd (LSE:BTC, OTCQB:VINZF) jumped 10% to 1.6p after it reported a rock chip sample grading 143.1 grams of gold per tonne from its Amonett-Frank project in Nevada, the highest grade returned so far across its US portfolio. The main market-listed company, chaired by David Lenigas, has been building a gold exploration business alongside its bitcoin mining operations.