I'd like to add that big tax increases (if not off set by loopholes, tax credits, work arounds, or other such things) generally will lower investment on mining activities unless demand for those minerals is so high and alternatives so short that people have no option but to pay. Generally, I'd be more in favor of intelligently designed royalty agreements where the amount of royalty due to the state per unit output varies according to the market price of the mineral in question. That way the mines stay profitable (and people employed) no matter if the price of the commodity goes up or down but if the price goes up then so does the amount of the state makes off of these sales.
This has become very common in oil royalty contracts but I haven't heard of such complex royalty agreements in other materials mainly because they're much more common on Earth (iron, tin, etc...). The big problem with saying we're just going to tax you X% depending on your profits is it undermines the incentives companies have to become more efficient producers while a sliding royalty rate agreement (pegged to market prices) insures the state makes more if the commodity in question's price goes up (and less if the price goes down) but the company still has an incentive to be as efficient as possible because increased efficiency still means higher profits.
This has become very common in oil royalty contracts but I haven't heard of such complex royalty agreements in other materials mainly because they're much more common on Earth (iron, tin, etc...). The big problem with saying we're just going to tax you X% depending on your profits is it undermines the incentives companies have to become more efficient producers while a sliding royalty rate agreement (pegged to market prices) insures the state makes more if the commodity in question's price goes up (and less if the price goes down) but the company still has an incentive to be as efficient as possible because increased efficiency still means higher profits.
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