While loading a bag of rockdust, the employee felt pain in his back. He worked the next day and began a 2 week vacation period on 6-26. He missed work on 7-12 & 7-13, but did not indicate to management that it was work related. He came out of the mine complaining of back pain on 7-21, scheduled a day off with the mine clerk for 7-22, but began missing work on 7-23.