Primary succession happens in a place where there is no soil cover or it is removed.
an abandoned field- Secondary; because there is cover of soil left, even if vegetation is removed.
a cooling lava flow- Primary; volcanic events lead to loss of soil layer, so this would lead to primary succession
a valley under a glacier- Primary; retreating glaciers are lead to primary succession
an unused farm-Secondary; the soil cover is still present
a burnt forest- Secondary; soil cover is still left for vegetation to start over again
a deserted mine- Primary; because there would be barren rocks left, so soil would be formed by pioneer species first.