The golden pickax was an ancient, extremely holy relic of the cult of the Stranglers which featured prominently in Water Sleeps. It was lost to the Stranglers and effectively inherited by the Nyueng Bao. The object turned out to be a priceless shadowgate key. At first glance, it was initially mistaken to be a war hammer, but only because a crumbling, cast-iron outer shell concealed the object's true shape.
Although the pickax was not mentioned in the Annals of Bleak Seasons, later revelations would expose that the relic played a major role in those events. Sometime during Bleak Seasons, Soulcatcher stole the golden pickax from the Nyueng Bao priests at the Vinh Gao Ghang Temple of Ghanghesha, where it had been kept for generations. During her time with it, it was still covered with its sheath of cast-iron, and even the champion sorceress could not identify the underlying pickaxe. Using the artifact, she safely crossed the shadowgate, traversed the glittering plain, and entered the fortress with no name. There, at the feet of the immortal but immobile golem Shivetya, she tinkered haphazardly with the machinery that Shivetya used to maintain the sorcery of the plain. Her careless activity caused the gigantic earthquake that occurred at the end of Bleak Seasons. It created fissures not only on the plain, but also reached back into the homeworld, where the quakes took thousands of lives. The most devastated city was Kiaulune, geographically the closest place to the shadowgate.
Later, the pickaxe was stolen from Soulcatcher's compound by Narayan Singh, the most notorious Strangler jamadar. Narayan's goddess, Kina, clouded Soulcatcher's mind to permit the theft. He hid it inside the Strangler temple within the Grove of Doom.
Narayan Singh turned over the pickax to Sleepy (the Annalist of the Black Company) in exchange for the partially-transcribed Books of the Dead. When he retrieved it from inside the Stranglers' temple at the Grove, he accidentally dropped it, creating a crack in the iron shell. The older son of Iqbal Singh pointed out the deep crack. Iqbal pried away some of the iron, and for the first time in centuries, the gold underneath was visible.
Later, One-Eye and Goblin chipped away the iron shell entirely. Some of the ancient lettering on the pickax resembled the alphabet of the very first Annals, the "Book of the Company", as well as the first of the Books of the Dead. When they showed the relic to their captive, the Daughter of Night (who was Kina's "Foretold" messiah), she reacted desperately and attempted to seize the object despite immense personal pain. This proved without a doubt Sleepy's educated guess that the relic was originally a Strangler artifact.
Sleepy, Tobo, and the rest of the Company and their allies then used the artifact to exit the homeworld by crossing the shadowgate. They safely traversed the glittering plain because the pickax, functioning exactly like the Lance of Passion, provided the necessary magic shield of protection against the millions of lethal shadows on the plain. Sleepy brought it inside the fortress with no name, where she finally located the Captured, who had been trapped for 15 years in the cave of the ancients. There, they also recovered the Company's Lance of Passion (another shadowgate key) but that one was soon lost by Goblin when he impaled Kina with it.
After liberating 5 of the Captured, Sleepy then used the pickax to bring her band safely across the shadowgate of Hsien, where the Company created their new headquarters, the Abode of Ravens. She made several expeditions with the pickax back and forth between the fortress and the Abode of Ravens, liberating small groups of the remaining Captured each time, until they were all freed.
The pickax was discussed briefly in Soldiers Live by Tobo and Croaker. Tobo stated that he left the object with Shivetya at the fortress with no name, and it is not mentioned again. Its usefulness as a shadowgate key was superseded by Tobo's 10 brand new keys, and, any ability it may have had to liberate Kina was nullified after her defeat at the hands of Croaker and Goblin.