Siderite is an ore of

Explanaiton:

Siderite is a mineral composed of iron (II) carbonate (FeCO3).
It is a widespread mineral that is an ore of iron.
The mineral commonly occurs in thin beds with shales, clay, or coal seams (as sedimentary deposits) and in hydrothermal metallic veins (as gangue, or waste rock).

Final Answer:

Siderite is an ore of Fe.  Hence, option D is correct.