well of course if you removed the cable from the battery its not sparking... i dont think ground was neccisarily the problem though... i'd look for a bare wire or something else shorting on your block before you run into some much worse problems down the road... like an engine fire.... the sparking was caused by something energized hitting a ground... which would most likely be your block that was the ground... and a wire/coil/something shorting on to the block