As metallurgic techniques expanded over Europe since the Chalcolithic, prospecting probably relied importantly on familiarity with the on-look of potentially metal-rich superficial deposits either by checking directly or asking locals. By identifying ores thanks to their general aspect (as malachite or azurite for copper, magnetite or haematite for iron, etc. for silver, tin, lead, etc.), prospectors could find a suitable place to begin mining.

There was probably, of course, a fair deal of trial and errors over several centuries, small and accessible deposits being quickly exhausted, failed attempts, deposits forgotten for any reason, etc. and of course metal deposits whose existence was simply ignored or dismissed due to their lack of accessibility (as a fair deal of Bohemian deposits even while the region was a metallurgic centre for the Iron Age) as well as 'success stories' of important mining site being exploited over decades or centuries as the Great Orme mines in modern Wales that utterly dominated insular copper extraction, with territories being known from being more ore-rich than other and possibly triggering small migrations or movements as from mainland or Britain to Bronze Age Ireland.

Gaul itself, in its classical limits, wasn't necessarily a great mining hub in the Copper and Bronze Age. Even while copper and tin mines were especially worked (respectively over the Mediterranean arc and the Atlantic facade) along with gold, lead or silver deposits,it seems that both Iberia, British Isles or Bohemia would have been overall more important in the production and trade of metals in Bronze Age Europe. While it might be caused by archaeological myopia giving a lack of so far evidenced data, it appears that the Iron Age as a period of important mining development in the Hallstatt and La Tène horizon (i.e. regions generally associated with Gauls in France, Benelux, southern Germany and Czechia), especially so in the last two centuries before the turn of the common era.

Iron mining is by far the most evidenced for in Gaul which was for all intent and purposes the land of iron in Antiquity, since the late Hallstatt, but gold mining was seemingly an important affair too, Strabo describes the metal as abundant in Gaul, before being significantly downgraded after the conquest.

Lead and argentiferous lead, both metals having only a limited indigenous use, remained fairly marginal (especially in comparison to Iberian and British mining) and really became more common in the Roman period onwards only.

It's not clear how much tin and copper were worked out : tin mines of Brittany and especially Limousin might well have been exploited since the Iron Age but without definitive evidence before the Ist century BCE, and while there literary mention of copper mining in southern Gaul before the conquest with mostly small mines evidenced for even after the Roman conquest although in bigger numbers than previously thought.

Other materials could be searched for, as sapropelite for jewel-making in western Europe : originally produced in Bohemia but by the IInd century extracted in central Gaul and southern Britain as well. Finally, while there is not known example in Gaul itself where it was harvested on the coast, salt mining as evidenced for Durnberg and Hallstatt.

Even while the techniques used by LaTenian populations could be fairly sophisticated, there's no real reason to attribute them an exclusively indigenous origin : rather it would have been part of a technical set both inherited and borrowed from earlier periods and neighbours. The comparison with Roman Spain or pre-Roman Britain mining techniques comes regularly, which hints at propagation of techniques over western Europe maybe as far as the Early Iron Age but firmly interconnected even until the turn of the common era with technological diffusion.