First, translate your lat-long coordinates into X-Y coordinates, such as UTMX and UTMY, so that both are expressed in the same units. Then ask proc mixed to fit a spatial covariance structure to your data with
random intercept / type=sp(pow)(utmx utmy);
also consider type=sp(sph)(utmx utmy) or type=sp(exp)(utmx utmy), (the choice will probably not matter much).
hth
PG