This work studies the problem of GPU thread mapping for a Sierpinski gasket fractal embedded in a discrete Euclidean space of n x n. A block-space map lambda : Z2E -> Z2F is proposed, from Euclidean parallel space E to embedded fractal space F, that maps in O(log2 log2(n)) time and uses no more than O(nH) threads with H approx 1.58... being the Hausdorff dimension, making it parallel space efficient. When compared to a bounding-box map, lambda(omega) offers a sub-exponential improvement in parallel space and a monotonically increasing speedup once n > n0. Experimental performance tests show that in practice lambda(omega) can produce performance improvement at any block-size once n > n0 = 28, reaching approximately 10× of speedup for n = 216 under typical block configurations.