In compiling Welsh mining word lists there will be some that differ materially between north and south Wales, reflecting the more general north/south linguistic divide.
The anthracite coal mining area of West Glamorgan and East Carmarthenshire had many specialist Welsh terms not used in the remainder of the south Wales coalfield. This reflects the different nature of anthracite ['glo carreg' = stone coal, relfecting its hardness] to bituminous coal and the resulting different working techniques and hence specialist vocabulary.
A couple of coal mining terms from south east Carmarthenshire that I can recall:
bradish = towing belt
sten [with a roof-shaped accent on the 'e'] = water jack
uwch ['sow'] = bell stone
As someone observed earlier on this thread, quite a few words are transliterations from English. They are however accepted as the correct Welsh version. English has been such a dominant language that numerous examples of loan-words for technical terms and new objects are inevitable. Welsh is certainly not the only language so affected - virtually every language has borrowed from English.
The widepsread adoption of Cornish terms in the field of non-ferrous metal mining, commented on in this thread, is a good example of how a technically dominant linguistic group results in their terminology becoming widely adopted.
At least one Welsh word with a strong mining connection was adopted abroad. Silica bricks for furnace linings were developed in the early C19 at the head of the Neath Valley using silica rock from the outcrop at Craig y Ddinas ['City Rock' - legend says that Arthur lies beneath it, awaiting a call to arms to battle the Saxons], worked from quarries that soon became mines. The trade name 'Dinas' [in Welsh, 'd' mutates to 'dd' after a vowel, or an auxilary vowel such as 'y', hence the slightly different spelling] became the generic name for silica bricks and silica rock. With the Welsh iron and non-ferrous smelting industries being internationally pre-eminent in the early and mid C19, the term was widely adopted abroad. The result was that the word for silica rock in French, German and Russian was, until the 1960s (when more technically precise terms were substituted), 'dinas'.