What is the minimum clearance required between a buried gas pipeline and buried XLPE cable crossing more than 45deg angle?

It usually depends upon where the crossing is located, the best authority is the owner of the pipeline, they may have requirements that take into account the local conditions.

Just off-hand, I'd say that this is one of those situations where "more is better" applies. Like the old saying, "if one will do, why not two!" Mr. Maltz has the correct answer, however.