The simple answer to your question is no. As you can see from my amendment above, the second part should not stand alone as it is not a complete sentence. I have removed the full stop and replaced it with a dash, then a lower case "m". The single two-part sentence is now fine.
Also note that I deleted the word "of" in the first part. We "point out" something. You do not need to capitalise the word "mining" unless it is at the beginning of a sentence or the beginning of a quote.
You don't really need the word "activities" either, although I have left it in. You could have just said "... the disadvantages of mining - mainly, ..."
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