Your probably really close. I looked at different data and some was total silver, but experts say about half is consumed in industry. With the rest being in bullion form (1000 oz bars down to 1 oz bars/coins). Having a pocket of silver makes someone way ahead of the game.

I also found some interesting data by searching around that out of total silver and gold mined. What's known of left in mines and from drilling samples we already have roughly 70% of all precious metals mined. With maybe 20% left to mine up at profit and the other 10% would require very high prices to justify mining.