I only have a very basic knowledge of the Second Boer War (if any at all) and I would like to study it in greater detail, but as the question states, would it be fair to say that the main reason for the British invasion of the Transvaal was because they wanted to get their hands on the gold mines?
Sorry if it is a stupid question but I suppose asking questions is the best way to learn
I think that is part of it. We can't take this in isolation either. By 1899 the Boer republics were essentially surrounded on all sides by European colonies. Africa itself was becoming smaller and smaller, and territory (and resources) to exploit becoming scarcer. The expansion north into modern Zimbabwe just prior to the Second Boer war was driven by finding more gold mines to exploit, and the disappointing volumes that those mines could produce meant that the Boer Republics not only controlled some of the last 'free' territory in Africa, but also some of the richest.