If you economy is booming you could argue you do not need the revenue from a mining industry, in an area of poor employment, seasonal jobs and low wages that is far from the case. Crofty currently employ 50 people on more than the average Cornish wage, the great majority of the employees are locals - do we need it - boy do we! If you don't want it in your area, well fine.
The finance for mining operations does not come from traditional borrowing sources (i.e. banks) as it is too high risk for them. Instead the finance comes from mining finance houses, with investrs who understand the risks, but reap the rewards. In the current economic climate there is more money from these investment sources as investors look for somewhere else to invest money as opposed to conventional investments due to the very low returns. hence crofty have £85 million pounds of funding to finance reopening and Hemerdon $(Aus)150 Million.
No mining operation would base their business plan on the current exceptional prices, Croftys business plan is based on a tin price of £3000 per tonne, the extra is a bonus, hence a sustained fall in the price of tin would do the mine little harm, in fact a fall to around $18,000 per tonne would probably be welcomed to deter exploration elsewhere.