How do I get collect silver in the mine when there is lava?

It depends on your level and the tools available to you.

I'm L54 and have access to the 'Iron Pick' which collects all iron off the board, the 'Drill', which collects all rocks and iron together at once, the 'gas lamp', which collects all gas at once, 'Flint' which turns all gas into rubble, and the 'Water Pump' which collects all lava off the field.

Otherwise you can collect one lava with one turn, but I'm not certain what level this begins at? Try it I guess..?

Edit:

Apologies, got confused with Iron (which makes Silver from long chains), but it's the same process, you get a Silver pick to collect all silver and can also use a 'Silver Transmuter' to change coal into silver.

Apologies for the iron confusion before.