Statue like effect

is this a stone statue? or a bronze/metal statue?
Depending on which is it, just follow the usual process for it.

Well, if you want to make a Tau who LOOKS like a statue, or make an actual statue from a Tau ethereal, there some options.

Though there are some good tutorials about painting marble-stone effects; Really spectacular.

The simple approach which I have used on a Galdriel model would be as follows -

Undercoat in black
Base coat of codex grey
drybrush in skull white with highlighting where you judge as well
Wash in black/dark ink

Provides a quick and reasonable look if you're just after table top quality

Roughcoat + heavy drybrush of chadron granite + normal drybrush of codex grey + final light drybrush of skull white

For a verdigris [oxidized copper] effect you could start with a Dark Green & gradually dry brush to a Pale Green...pigeon poop is optional.

I have made some nice statue effects for stone with zombie flesh drybrushed VERY lightly as a highlight for a moldy effect. I think it could be used for oxidized copper as well!

Or,
White prime, Jade Green base coat and heavy drybrush Brazen Brass