The correct answer to this open question is the following.
The conclusion I can draw about Brandt knowing that he continued his search for precious metals after most Jamestown settlers were involved in agriculture is the following.
It seems that Sebastian Brand continued to believe that he could find precious minerals such as silver, copper, and gold in the Jamestown colony of Virginia. He maintained his hope for the great discoveries of precious rocks that he wrote a letter on January 13, 1622, to Henry Hovener, who was a merchant from the Netherlands that at the time was living in London, England.