Here are some suggestions on how to handle this.
1) Using information dowsing ask how far up from the ground the top of the vein is.
Stand at the wall at the quartz location. Leave enough room for your instruments to move freely.
Ask at 1 foot increments until you get a yes answer from your instruments.
An example question would be: Is the top of the gold vein at least 3 feet above the ground?
Let's say the instrument says "no", then ask again is it 4 feet? no, 5 feet? yes. Now you know the approx. distance to the top of the vein.
2) This is not as accurate as #1 but something you may want to try.
You can walk perpendicular very slowly from or to the wall where the quartz is that your instrument pointed out to you, thinking about the distance from the ground to the top of the gold vein. Just dwell on "distance from the ground" in your mind but don't ask for specific numbers as you did in example #1.
When you get your "yes" answer, the distance from there to the base of the wall is the approximate distance to the top of the vein from the ground at the base of the wall. If you choose to walk towards the wall, then start your walk further than 12 feet away, I'd go at least 15 feet away and walk slowly towards the wall. Let's say you get a "no" answer until you get about 5 feet away from the wall, then you know the top of the vein is roughly 5 feet up from the ground at the base of the wall.
3) Is there a way to get above the vein? If so, then use information dowsing again to determine the depth from where you are standing. Just phrase the question as: Is the top of the gold vein at least 5 feet below the ground? no, 7 feet? no, 10 feet? yes. Now you know how deep to go to get to the top of the vein.
4) You may also use information dowsing to find out how far the gold is from the face of the wall into the rock.
Just change the phrasing of your question: Is the gold at least 3 feet from the face of this wall?, ect.
Hope this helps,
Jon