I could not tell you what to do,but here are some observations.Usually the share price drops after a rights offer as then there so many more shares in circulation and some holders buy or if connected to the company in some way get the shares cheaper.Soon ad the issue hits the market and drops a couple of cents those people also sell forcing the price down further.In the medium term MTX should do well as there is a immediate shortage of copper .How ever in about two years time there will be adequate supplies.Hopefully the Congo will be stable,they have not a good record in political inteference in mining.In the past they destroyed Anglos copper projects,which lead to the mines closing and a depression there.
A rights issue is only available to existing shareholders for the purpose of investing additional capital into the business in order to fund their proposed re-structuring. The discount that is offered usually outweights the extent at which the share price falls after the rights issue. There may be more shares in issue, but there is also more cash asset in the company from the issue - these should outstrip one another. If the price falls as low as 360 after the issue, and you believe in the proposed re-structure, simply an opportunity to buy a whole lot more that your rights at the same price. Rights are supposed to be tradable too - I don't know how that works thought through the STRATE system.
The Rights to the shares will first be traded as Nill paid letters, under the code MTXN. shareholders accounts will be automatically credited with their entitlement. These rights can be Traded on the market. The value of the Rights will be determined roughly by the differential between the share price traded on the market eg 372 and 3.60 = 12.