Tips, tricks & notes:

• The mining carts go both ways, which means when you're doing tasks for the companies, you can mine in the dwarven mines, and then take the carts back to Keldagrim. You can also smelt the bars in Falador using this method.
• A good method for quickly earning the favour of a mining company is to take many of a single type of ore which might be requested (clay, for example). Each time a task is shown which does not involve your chosen ore, simply walk away from the conversation without passing the screen where your task is shown. As long as you walk away without passing that part of the conversation, you should lose no favour.