Kind of. Red clay is high in iron oxide (iron-oxygen) and seems to be the big one. It's identified as Fe203, which is why detectors like the Fisher F5 shows an on screen Fe meter. (Fe=ferrous).
I'm sure there are other minerals, like salt, that affect depth. If in doubt, ask someone on this forum that may live close to you. If you still are in doubt, the Bounty Hunter Platinum is a step up from the Delta at about the same price. It is a Teknetics Gamma without the Fe meter and manual ground balance, but is the same platform as the Gamma and has Ground Grab auto ground balancing (It's not a fixed GB like the Delta). The other difference is not being able to use the Greek coils. The Gamma is my choice of an ideal mid range detector.