By the second quarter of the 18th century, a number of private coal pits were operating on a commercial scale in coalfield located the area we now know as Midlothian.  Miners immigrated to Chesterfield from Wales, England and Scotland.  The Wooldridge family from East Lothian and West Lothian in Scotland was among the first to undertake coal mining in the area.  It is likely that the mining community was eventually named after their Mid-Lothian Mining enterprise, a combination of their two home town names.  The Heths, beginning with Colonel Henry "Harry" Heth (died 1821), who emigrated about 1759, who were English investors, opened coal pits in the county.

According to records held by the Library of Virginia, on January 25, 1832, Beverley Randolph, John Heth, and his younger brother, Beverley Heth (1807–1842) petitioned the Virginia General Assembly for the first coal mining corporation to be chartered in Virginia.  After substantial opposition to the concept, this was accomplished the following year with the incorporation of the Black Heath Colliery.

Coal mining at Black Heath was both difficult and dangerous work, and there were fatal explosions.  On March 18, 1839, 40 men, mostly African American slaves, were killed in a 700 foot shaft at the Black Heath mine.  On June 15, 1844, a mining explosion at Black Heath killed 11 more men.  After the second incident, the mine was closed until 1938.

Source: Wikipedia

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Dreadful Accident
Adams Sentinel, Gettysburg, Pennsylvania
March 25, 1839

We learn from the Washington Globe that on Saturday night an explosion took place in Heth's Pit, (a coal mine situated about 12 miles from Richmond, Va., in the county of Chesterfield,) by which it is said that sixty-three negroes have been killed or buried alive.  The shaft is 800 feet deep -- deeper, probably than any other in the United States -- and as the falling in of earth has been considerable, there is no probability that any of the persons below, if now alive, can be extricated.

A Postscript in the Richmond Compiler of Tuesday, attached to an account of the accident similar to that related above, says --

"Since the above was in type, we have just conversed with a gentleman from the Pit.  He thinks that between thirty and forty had gone below before the explosion -- four of them had been gotten out, who, it was supposed, would recover -- two others were seen dead; and cries and groans were distinctly heard from some who had not been reached.

So great was the consternation and dismay that the accuracy of details could not be relied on; and so great was the terror among all in the vicinity, that the proper efforts could not be promptly made to get out the unfortunate laborers."

One of the three at the mouth of the Pit, alluded to above, is living with both legs broken.  The other two were immediately killed.  The shaft and engine are but little injured.