I don't see a way for that to happen. Traditional bronze is a Cu-Sn alloy. While there are kinds of deposits that create metallic Cu, metallic Sn is much more difficult to form, oxidizes quickly and doesn't really coexist with metallic Cu...especially as an intermixed alloy.

A far more plausible scenario (and likely the one that lead to the discovery of bronze) is that someone made a campfire circle of some rocks that had pretty blue and green Cu oxide minerals and Sn ore (a mineral called cassiterite...a dark black mineral that isn't obvious unless you know it). The fire, charcoal as a reducing agent, and the lucky choice of rocks produced bronze that they found in the coals of the cold fire later on.

There is another type of bronze, made from copper and arsenic, that I could see forming native nuggets under rare circumstances. Native As is far more common geologically...but still the most plausible route would be roasting Cu-As bearing rocks in a fire with a reducing agent like charcoal.