Steve Curtis, chief executive, said the improvement underscored the overall confidence level in Blanket's resources.
Total measured and indicated gold ounces now amount to 714,000 ounces compared to 671,000 ounces at the end of 2016.
Curtis added the miner is modifying the life-of-mine plan at Blanket to include the additional ounces where possible with a view to extending its life.
Caledonia owns 49% of the mine and is midway through a major expansion that includes a new central shaft.
There was a slight reduction in the average grade to 3.98g/t from 4.31g/t, but this grade remains well above what is being processed currently.
Inferred resources, a less certain classification, rose by 47% to 887,000oz or 5.53mln tonnes at a grade of 4.99g/t.
The miner added resources at Blanket have now risen for six sixth successive years since 2011 even though over 250,000oz of gold had been dug out during this period.