that's an argument which works for capital goods (like livestock) but not for what Henry George considered to be natural opportunities of fixed supply like lithium ore (and land in general).

Henry George, if he were still alive today, would probably say that valuable raw mineral deposits like this would be more likely to be discovered and brought into productive use earlier if they were taxed. The argument being that people would have no reason to speculate on a large untapped reserve of it. There would still be an incentive to bring it into production because the earned profit would be made through extraction, processing, and distribution of the material even if the higher holding cost of the land is factored in as a cost.