Turns out convict leasing has a Revolutionary War-era ancestor.
As hundreds or even thousands of enslaved people began running away to seek protection from the British military, the southern colonies wanted to make an example of the runaways they caught. But executing them proved costly since the government was required to compensate their owners.
According to historian Sylvia R. Frey, the Virginia colony found a profitable alternative:
Hard labor in remote Fincastle or Montgomery county mines had the clear advantage over execution of removing potential trouble- makers without substantial cost to the state. At the same time it provided a work force to produce lead for cartridges, of which the state was "in extreme want." Throughout the Revolution numbers of slaves, some of them "merely suspected of a design to ... escape" to the British, were escorted under heavy guard to the mountainous western region of (Virginia) to labor in the lead mines. Others were put to work making saltpeter, so they could perform useful service without causing further trouble.
You can check out her full article Between Slavery and Freedom: Virginia Blacks in the American Revolution (Available through the Houston Public Library or with a free JSTOR account).