'Pay streak' definitions:

Definition of 'Pay streak'

From: GCIDE

Pay streak \Pay streak\
1. (Mining) The zone, parallel to the walls of a vein, in which the ore is concentrated, or any narrow streak of paying ore in less valuable material. [Webster 1913 Suppl.]
2. (Oil Boring) A stratum of oil sand thick enough to make a well pay. [Webster 1913 Suppl.]