What is the value of a 1901 ten dollar Liberty head gold coin with an D mint mark?

Please look a bit more closely. The mint mark is almost certainly an O for New Orleans. The Dahlonega Mint closed in 1861 and Denver didn't open until 1906 so a 1901-D coin is not possible. OTOH if the mint mark is truly a "D" it's almost certain you have either an altered coin or a counterfeit, and it would need to be inspected in person.

Assuming it's genuine its value would be a close to that of 1/2 oz. of gold, depending on how much of the coin is worn off. As of 09/2008 that's somewhere between $485 and $545.