It appears a horse following Point Proven was "caught up in the incident and couldn't avoid the fallen horse" Purcell added.
Race eight on the card was a flat race, conditions were good and "unfortunately it's one of those terrible incidents. After the investigations are completed we'll know more," he said.
Two of Black's children were at the raceday.
Officials will have extensive video coverage of the race, which will go into the various inquiries, and all jockeys will be interviewed.
Black is the second jockey in 10 years to have died during a race in New Zealand, after Gold Coast jockey Ashlee Mundy at a race in Kurow in December 2012.
"The racing industry is a very tight knit community and rallies together with great strength and support during these tragedies. Clearly a lot of people are impacted."
A study on safety equipment for jockeys will be made, but Purcell doubted the coroner will get into great detail on that aspect.
"In New Zealand we adapt world best practice," he said.
"For more than a decade jockeys have been required to wear safety vests and helmets have been compulsory for decades to an appropriate international standards.
"But that's only part of it. The reality is despite those measures this incident occurred."