The phrase "a small portion was" is correct and usable in written English.
It can be used when referring to a specific, limited amount of something in a past context.
Example: "During the meeting, a small portion was allocated for discussing future projects."
Alternatives: "a minor part was" or "a limited amount was".
The majority of the recA-dependent excision repair was recF dependent, and a small portion was recB dependent.
Our camp was stocked with cases upon cases of lemon-fresh Joy, but only a small portion was ever used for washing dishes.
A small portion was kept permanently by the farmer and his family, but most of the land reverted to the state for redistribution upon death or retirement.
Only a small portion was left but again, it wasn't until I asked a policeman how many children had been in the school and he replied "about 200" that the full horror hit us.
By the time Turner died, in 1851, his estate, administered in part by his friend and admirer John Ruskin, was valued at $140,0000 (about $6 million today), of which the Royal Academy received $20,0000 (about $840,000); a small portion was set aside to honor the artist's wish to have a monument to himself erected in St . Pauls Cathedral.
Facebook also removed almost 2,000 pages, groups and accounts for spam - "of which a small portion was engaged in coordinated inauthentic behavior" - linked to Russia".
A small portion is within the Town of Southold.
The overwhelming majority of his constituent mail is now about the far-out ideas, and only a small portion is "based on something that is mostly true".
Though the island measures about 25 miles in length, it is less than 2 miles wide at its broadest point, and only a small portion is inhabited.
So even if only a small portion are put back, some analysts argue, the losses for banks could run into the tens of billions.
