Given the task definition and input, reply with output. This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.

Passage: The cause of the conflicts was like many of the Indian Wars. In 1684, the Spanish colonists in the present day Mexican state of Sonora discovered silver in the Rio Yaqui Valley. Following this, the Spanish gradually began settling on Yaqui land, and by 1740, the natives were ready to resist. Some minor conflicts from before dated back to 1533 but in 1740 the Yaqui united with the neighboring Mayo, Opata, and Pima tribes and successfully drove the colonists out by 1742.
Question: Where was silver discovered?
date