Yes and no. High temperatures will heat up the ground, which should be a concern for you if you're detecting in mineralised soil, because you'll notice the detector becomes more 'chattery'. You can fix this by ground balancing the detector, so it adjusts to the soil. If you don't ground balance, the depth of the detector doesn't *decrease*, but you may confuse deep targets with mineralisation messing with your detector.
Especially if you're gold prospecting in hot, mineralised ground, you want the machine to be ground balanced as best as possible so you can hear those faint whispers which might be small gold nuggets.