Metal is extracted from ore by heating it to a liquid state. So, liquify the metal without heat. I estimate this to be a Rego Terram effect: the caster is changing the metal from one natural state to another, so Level 1, plus 2 magnitudes for metal. Base level: 3.
Range touch works fine.
Changing a solid to liquid for a moment does not give time to drain from the surrounding rock, so increase the level a magnitude to at least diameter, Level 4. Sun duration may be smarter, to let the whole mass of ore drain completely.
The individual size for base metals is a cubic foot, and for precious metals 1/10th of a cubic foot. In either case you'll want to increase it one target size, so minimum Level 5.
So, something like:
Liquify the Base Metal / Blood of Mars (iron) / Tears of Venus (copper) / (something appropriate for tin or mercury) ReTe
R: Touch D: Diameter T: Group
Changes a base metal from a solid metal to a liquid metal. Metal mixed with another material (for example, in an ore) will either drain from the material or pool in it, and some stirring may be needed to separate the metal from the other material. The amount affected is up to 10 cubic feet of mixed material.
This specific spell works only on one base metal: iron, copper, mercury, tin, or lead. Other spells of identical effect are needed for other base metals. A similar effect can be used to liquify precious metal, either silver or gold, but at 1/10th the target size (so, 1 cubic foot).
ReTe Base 1, +2 for metal, +1 for Dia., +1 for Group / increased size
I would push it up a bit to Sun, and probably enchant it into a crucible-like bowl. Some agitation and pour-off over the course of the day will get the metal out.