We should not be surprieed to hear by some arrival of the capture of the mines of San Luis and Zacatecas by two columns of Gen. Scott’s army, under special instructions from the War Department. We understand the expeditions were about to be organized for this purpose when the last official letters left Mexico for Washington. If we may believe the letters from the camp, written even before these expeditions were suspected, the effect will be to deal another heavy blow at the enemy, by cutting him off from some of his material resources. To show what were the speculations upon this subject, we lay before our readers the following extracts of a letter published in the last New Orleans Commercial Times, from a correspondent in the city of Mexico, of the 1st of December: